can someone correct these. and help me

DIrections:Factor

(3) 4x^2-4x-15

My solving: 4*x*x-4*x-15 (the star means multiply
my final answer: x^3-15 (the ^ means for exponent)

(4) 5x^2-26x+5

my solving: 5*x*x-26*x+5
my final answer: x^3-16

I don't understand what you did. The question asks for factors.
(2x+3)(2x-5)
Check that.