Along border 2x + 3y = 240.

(x,y) at corner points are (0,80) & (30,60).

p=0.5x+0.4y

At (0,80), p=32.

At (30,60), p= (0.5*30)+(0.4*60)=15+24=39.

Profit is maximized at $39 when sliderule sales are 30 units and sweatshirt sales are 60 units.

{I've seen the importance of plotting graphs to understand this concept. Thank you Romsek!}