D and E I believe would be the correct choices, 7x4 gives you 28 and 7x7x7x7 gives you 2,401.
15. 2x-5=-20
2x=-15; Add positive 5 on both sides to isolate x.
x=; Divide 2 on both sides to find the value of x.
17. =-9
9x=-36; Multiply positive 4 on both sides of the equation.
x==-4; Divide 9 on both sides of the equation to find the value of x.
Wait until your 16 so you don't get into trouble