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