Answer
See the detailed answer below.
Work Step by Step
$$\color{blue}{\bf [a]}$$
Here is the table of the possible outcomes of the 3 coins experiment.
\begin{array}{|c|c|c|}
\hline
\text{Coin A} & \text{Coin B} & \text{Coin C} \\
\hline
H & H & H \\
\hline
H & H & T \\
\hline
H & T & H \\
\hline
H & T & T \\
\hline
T & H & H \\
\hline
T & H & T \\
\hline
T & T & H \\
\hline
T & T & T \\
\hline
\end{array}
$$\color{blue}{\bf [b]}$$
From the table above, it is obvious that we have 8 rows that represent the 8 possible outcomes.
We can get two heads and one tail 3 times out of 8.
Thus, the probability of getting two heads and one tail is
$$P_{\rm HHT}=\dfrac{3}{8}\times 100\%=\color{red}{\bf 37.5}\%$$
$$\color{blue}{\bf [c]}$$
From the table above, the probability of getting at least two is
$$P_{\text{HH at least} }=\dfrac{4}{8}\times 100\%=\color{red}{\bf 50}\%$$
