a = 9∧-7
The second variable of the first question (9∧-9) means it should be below the divide line, thus, becoming a denominator. Add it with the 9∧12. The bases are the same, therefore, we add the two corresponding exponents, as we are multiplying each variable. Then, simplify this into one fraction by subtracting the exponent of the demonimator, to the exponent of the numerator. The same applies to the second question.
b = 9∧-2
THE ANSWERS ARE IN BOLD.
I hope this helped :)