Perform the indicated operation?! HELP!

please help me do these problems!
1. (5x^3-10x+7) - (6x^3-20x+10)
2. (8x+3y) (2x-y)
3. (7a-5)^2

1.

(5x^3-10x+7) - (6x^3 - 20x + 10)
= 5x^3 - 10x + 7 - 6x^3 + 20x - 10
= -x^3 + 10x -3

2.

(8x+3y)(2x-y)
= 16x^2 - 8xy + 6xy - 3y^2
= 16x^2 - 2xy - 3y^2

3.

(7a-5)(7a-5)
= 49a^2 - 70a + 25

for the first one
remember to distribute the negative on the trinomial
for the 2nd one remember FOIL
for the third one remember the
(a - b)^2 = a^2 - 2ab + b^2

1) -x^3+10x-3

2) 16x^2-2xy-3y^2

3) 49a^2-70a+25