Answer:
x=10/-3, 4/5
Step-by-step explanation:
f(x) = (10 - 3x)(4 - 5x)
10-3x=0
-3x=-10
x=10/3
4 - 5x = 0
-5x = -4
x = 4/5
15x2 - 62x + 40
(10 - 3x)(4 - 5x)= 10 x 4 + 10 x -5x - 3x x 4 - 3x x -5x = 15x2 - 62x + 40
f(x) is a parabola, now you have to graph
