Algebra problem. Please help!

Question

7^3x * 7 * 7^x-1

Answer 1

when multiplying with like bases, 7 in this example, add the exponents.  

So 7^(3x) * 7^(1) * 7^(x-1) = 7^(3x + 1 + x - 1) = 7^(4x)