Well done for just crunching through the calculation the hard way, but remember in an exam, the number of marks available for a question should give you a clue how much effort is a good idea to put into a question, especially when there are other easier faster, or harder but doable and more lucrative questions to do first.
Didn't you spot the shortcut of factoring out 2^2 leaving 2^3 + 1. I.e. 3^2?