1) 15x^2 + 4 = 16x
15x^2 - 16x + 4 = 0
Use the quadratic formula: x = (-b ± √(b^2 - 4ac)) / 2a
x = (16 ± √((-16)^2 - 4(15)(4))) / 2(15)
x = (16 ± √(256 - 240)) / 30
x = (16 ± √16) / 30
x = (16 ± 4) / 30
x = 2/5 or x = 2/3

2) 7x^2 = 4x - 32
7x^2 - 4x + 32 = 0
This is a quadratic equation that can be solved using the quadratic formula, but the solutions will involve complex roots.

3) 5x^2 - 20 = 0
5x^2 = 20
x^2 = 4
x = ±2

4) 7x + 3 + 4x^2 = 0
4x^2 + 7x + 3 = 0
This is a quadratic equation that can be solved using the quadratic formula.

5) x^2 - 9x + 18 = 0
(x - 6)(x - 3) = 0
x = 6 or x = 3