a, 70 - 5 .(x - 3) = 45
⇔ 5 . (x - 3) = 70 - 45
⇔ 5 .(x - 3) = 25
⇔ x - 3 = 25 : 5
⇔ x - 3 = 5
⇔ x = 5 + 3
⇔ x = 8
b, 10 + 2x = $4^{5}$ : $4^{3}$
⇔ 10 + 2x = $4^{5-3}$
⇔ 10 + 2x = $4^{2}$
⇔ 10 + 2x = 16
⇔ 2x = 16 - 10
⇔ 2x = 6
⇔ x = 6 : 2
⇔ x = 3
c, 2x - 138 = $2^{3}$ . $3^{2}$
⇔ 2x - 138 = 8 . 9
⇔ 2x - 138 = 72
⇔ 2x = 72 + 138
⇔ 2x = 210
⇔ x = 210 : 2
⇔ x = 105