You can convert this to quadratic "form":

. . . . .

Factor this quadratic, and then solve the twoexponential equationswhich result.

This is the same sort of thing, except that the resulting equations will berational equations.

. . . . .

All you can do with this one, since you don't have a value for "a", is to move the unknown over to the right-hand side:

. . . . .

Then applythe Quadratic Formula, with the Formula's a = 1, b = 16, and c = -7 - a. (The two a's are different, obviously.)

If you get stuck, please reply showing how far you have gotten. Thank you!