A Skateboard manufacturer produces two models of skateboards, the FX and the ZX. The revenue for the firm is nonlinear and is stated as (number of FXs)($5 - 0.2 number of FXs) + (number of ZXs)($7 - 0.3 number of ZXs). The revenue is stated in $l,000s per week. The company has 80 labour-hours available per week in its shop. Each FX requires 2 labour-hours and each ZX requires 3 labour-hours. The anticipated demand for the FX and ZX are 20 and 15 per day. Formulate this nonlinear production planning problem to determine how many FX and ZX skateboards should be produced per week.