x = The number of members
450 / x = Each person's share
(450 / x) + 3 = Having gone up by three dollars
(450 / (x - 5)) = Each person's share minus the five deadbeats
(450 / x) + 3 = 450 / (x - 5)
Solve for x...
450 + 3x = 450x / (x - 5)
450(x - 5) + 3x(x - 5) = 450x
450x - 2250 + 3x² - 15x - 450x = 0
3x² - 15x - 2250 = 0
3(x - 30)(x + 25) = 0
x = 30, -25
The negative result is meaningless...
x = 30 members