a & b

$2 \times 3^a + b = 27 \cdots (1)$

$b=3^a \cdots (2)$

Sub $(2)$ into $(1)$ : $2b+b=27 \implies b=9$

Sub $b=9$ into $(2)$ : $9=3^a \implies a=2$

Hence $ab=2(9)=\boxed{18}$ .

2 x a^3 + b = 2xb + b =27 3b =27 b =9 = 3^a a =2 find axb = 2x9 = 18 Ans.

a=2 and b=9 the ans will be 18