Answer
(a)$A$
(b)$A/2$
(c) $3.75~millimolars$
Work Step by Step
We are given the function
$$R(s)=\frac{A s}{K+s}$$
(a) We have the limit
\begin{align*}
\lim _{s \rightarrow \infty} R(s)&=\lim _{s \rightarrow \infty} \frac{A s}{K+s}\\
&=\lim _{s \rightarrow \infty} \frac{A}{1+\frac{K}{s}}\\
&=A
\end{align*}
(b) We find the value of $R$ at $s=K$:
\begin{align*}
R(K)&=\frac{A K}{K+K}\\
&=\frac{A K}{2 K}\\
&=\frac{A}{2}
\end{align*}
Then the reaction rate $R(s)$ attains one-half of the limiting value A when $s = K$
(c) Since the limiting value is $0.1$, then
\begin{align*}
R(s)&=\frac{0.1 s}{1.25+s}\\
&=0.075
\end{align*}
Hence
$$s=\frac{(1.25)(0.075)}{0.025}=3.75$$
