Question

AAAAAAAAAAALLLLLLLLGUUUUUUEEEMMMM???

Answer 1

-1=log b 0,25
b^-1 = 0,25
1/b = 0,25
1/b = 1/4
b=4

Answer 2

$f(x)=\log_bx$

Do gráfico temos que: $f(0,25)=-1$, portanto:

$f(0,25)=\log_b(0{,}25)\\\\-1=\log_b(0{,}25)\therefore b^{-1}=0{,}25\\\\b^{-1}=\dfrac{1}{4}\\\\b^{-1}=4^{-1}\\\\\boxed{b=4}$