The plain language of SDCL 25-7-6.14 makes no mention of abating a "pro-rated" portion of child support based upon days actually spent with the children. Rather, the statute calls for abating a straight percentage "of the child support." the only "child support" contemplated by SDCL ch 25-7 is the monthly support obligation calculated according to the parties' combined net monthly income. See SDCL 25-7-6.2. "A trial court is given broad discretion when considering matters of visitation." Hybertson v. Hybertson, 1998 SD 83, P14, 582 N.W.2d 402, 405. Accord Weber v. Weber 529 N.W.2d 190, 191 (SD 1995). " 'However, the trial court's exercise of discretion is not uncontrolled and must have a sound and substantial basis in the testimony.'" Weber, 529 N.W.2d at 191 (quoting Williams v. Williams, 425 N.W.2d 390, 393 (SD 1988)). "The best interests of the child are to govern visitation matters, and a trial court's order will not be set aside unless an abuse of discretion is shown." Hybertson, 1998 SD 83 at P14, 582 N.W.2d at 405. See also Weber, 529 N.W.2d at 191 (trial court's decision can only be reversed upon clear showing of abuse of discretion). SDCL 25-7-6.14 provides: Unless the parties otherwise agree and the agreement is approved by the court, the court may, if deemed appropriate under the circumstances, order an abatement of not less than thirty-eight percent nor more than sixty-six percent of the child support if: (1) a child spends ten or more days in a month with the obligor; (2) the number of days of visitation and the abatement percentage or amount are specified in the court order; and (3) the visitation is actually exercised. The court shall allow the abatement to the obligor in the month in which the visitation is exercised, unless otherwise ordered. This Court recently reiterated the primary rules of statutory construction in Zoss v. Schaefers, 1999 SD 105, 598 N.W.2d 550: "Statutory interpretation presents a question of law reviewable de novo." Satellite Cable Srvs. V. Northern Electric, 1998 SD 67, P5, 581 N.W.2d 478, 480. One of the primary rules of statutory ... construction is to give words and phrases their plain meaning and effect. This court assumes that statutes mean what they say and that legislators have said what they meant. When the language of a statute is clear, certain and unambiguous, there is no occasion for construction, and the court's only function is to declare the meaning of the statute as clearly expressed in the statute. Zoss, 1999 SD 105 at P6, 598 N.W.2d at 552 (quoting South Dakota SIF v. CRE, 1999 SD 2, P17, 589 N.W.2d 206, 209).