Grace, remember that factors are things we multiply. The first term has 3 factors, 7, x, and x - 1.
The 2nd term has two factors, 5 and x - 1.
The 3rd has two, 2x + 1 and x - 1.
What's the only factor in common? x - 1.
7x(x - 1) + 5(x - 1) + (2x + 1)(x - 1) = (7x + 5 + 2x + 1)(x - 1) = (9x + 6)(x - 1)
Hope this helps!
