23.
5n^2 = 4n^2 - 4n
n^2 + 4n = 0
n(n + 4) = 0
n = 0 or n + 4 = 0
n = 0 or n = -4
24.
d^2 - 4d = 3d
d^2 - 7d = 0
d(d - 7) = 0
d = 0 or d - 7 = 0
d = 0 or d = 7
25.
3 - 13h = 3 - 8h + h^2
Subtract 3 from both sides.
-13h = -8h + h^2
Add 13h to both sides.
0 = 5h + h^2
0 = h(5 + h)
h = 0 or 5 + h = 0
h = 0 or h = -5