ab is 26.
If abb x 7 = 18ba then a = 2 (if a = 1 then the maximum value of abb is 199, and 7 x 199 = 1393 : if a ≥ 3 then the product would start with a '2' or higher number)
The equation now becomes 2bb x 7 = 18b2
b is therefore an even number such than 7 x b has a final digit of 2. The only number that satisfies this condition is 6 so that 7 x 6 = 42.
a is 2 and b is 6.