tolong bantuannya!!!!!

Soal 18 = C

[tex] = {( \frac{2 {a}^{2 - 1} {b}^{3 - 5} }{3} )}^{ - 1} \\ = { (\frac{2a {b}^{ - 2} }{3}) }^{ - 1} \\ = \frac{3 {b}^{2} }{2a} [/tex]

Soal 19 = D

[tex] = {( \frac{2 {x}^{2 + 3} {y}^{ - 4 + 5} }{3} )}^{ - 3} \\ = {( \frac{2 {x}^{5} {y}^{1} }{3} )}^{ - 3} \\ = \frac{ {2}^{ - 3} {x}^{5 \times ( - 3)} {y}^{1 \times ( - 3)} }{ {3}^{ - 3} } \\ = \frac{27}{8 {x}^{15} {y}^{3} } [/tex]

Soal 20 = D

[tex] {2}^{3x + 5} = {2}^{ - 4} \\ 3x + 5 = - 4 \\ 3x = - 9 \\ x = - 3[/tex]