a. (7^x)^9=7^81=
7^9x=7^81
9x=81
x=9
b. (8^5)^40=(2^30)^x=
2^600=2^30x
600=30x
30x=600
x=600:30=20
x=20
c. 10^13=50^13:x^13=
10^13=50^13:x^13; x ≠ 0
10^13=50^13/x^13
10^13 x^13 =50^13
x^13=5^13
x=5, x ≠ 0
x= 5
d. (20:x)^30=4^30
(20/x)^30*4^30
(20/x *4)^30
(80/x)^30
80^30/x^30