The profit function is given by:
p=25x-(10x+250)
the number of unit sold if the profit is 425
here we solve for x when p(x)=425
substituting the values in the equation we get:
425=25x-(10x+250)
425=25x-10x-250
solving for x we get:
425=15x-250
425+250=15x
675=15x
x=675/15
x=45
thus the number of units sold is 45