-9x^2 + 7x + 8 = 0
Note: One way to figure these out when they don't factor nicely is to use something called the quadratic formula. It works like this:
If you have an equation that looks like this: ax^2 + bx + c = 0
Then x = this:
x = (-b +- sqrt( b^2 - 4ac ) ) / 2a
For this problem a = -9, b = 7, and c = 8.
Plug those into the formula and you get this:
x = (-7 +- sqrt(49-4*-9*8))/2(-9)
x = (-7 +- sqrt(49+288))/-18
x = (-7 +- sqrt(337))/-18
The square root of 324 is 18 and the square root of 361 is 19. 337 is closer to 18, so let's approximate sqrt(337) as 18.
x = (-7 +- 18)/-18
x = -25/-18, 11/-18
x = 25/18, -11/18