Tamara subtracted -5x+9 from another expression and got 12x+a. when she subtracted 3x+4 from the same expression she got bx-7. from what expression did she subtract -5x+9 and 3x+4?

Tamara started with the expression of 7x - 3.

This is a tricky problem because each subtract problem only gives you a part of the expression.

In the first part, we can only determine the first term.  ? - (-5x) = 12  Therefore, the first part must be 7x.

In the second part, we can only determine the second term.  ? - 4 = -7  Therefore, the second part must be -3.

If you put the 2 parts together, you get 7x - 3.