-7w + 6 = 4w2
First put it into standard form:
0 = 4w2 + 7w - 6
The quadratic formula is:
x = [ -b ± √(b2-4ac) ] / 2a
In your equation, a = 4, b = 7, and c = -6. Plug those numbers into the quadratic formula and compute the answers (you'll get two due to the ±)