When multiplying exponential expressions 7^a and 7^b, you add up the exponents over the same base of 7. This works because the two bases are both 7
So, 7^a*7^b = 7^(a+b) is the answer
Notes:
1) I used the asterisk symbol instead of the 'x' to mean multiply. This is done so we don't confuse the 'x' with a variable.
2) Parenthesis are needed to indicate that all of the "a+b" is the exponent of 7
