To solve this equation, we first simplify the left side:

4129 + 7878 = 12007

12007 - 3127 = 8880

Now our equation is:

8880 ÷ (x - 3127) = 90

To solve for x, we can rearrange the equation:

x - 3127 = 8880 / 90
x - 3127 = 98
x = 98 + 3127
x = 3225

Therefore, the solution to the equation is x = 3225.