Multiply the numerators and multiply the denominators (top times top, bottom times bottom)
In your problem, 1 * 17 = 17 and (x^2 - 7) * 12b may be left written side by side.
This answer is:
12b (x^2 - 7)
If you had written a problem with factors in common, then you might have been able to reduce your fraction. Let me know if you need help with any of these kinds of problems.
Hope this helps.