Can someone correct these for me please...

Multiply. (x+2)(x-2)

My answer..x^2-4

Write in descending-exponent form, and give the degree

4x^5+x^8-7

My answer: In descending-exponent form would be: x^8+4x^5-7, The degree is 8

Multiply. 3xy^2(5xy-4x+6y)

My answer: 13x^2y^2+18xy^3

the first two are correct, the last is not You should have three terms. The first term will be 15x^ 2 y^3