log(x² + 21x) = 2

x² + 21x = 10²

(x − 4)(x + 25) = 0

4

$\text{log}_4\left(\frac{x^2}{3}\right)=2$

$\text{log}_2 \left(\frac{9x+2}{x^{2}-1}\right)=2$

3

See parts (a) and (b).