a)equivalent resistance in the circuit
b)total current in the circuit
c)potential difference across 30 ohm resistance

Dear student,

The equivalent resistance of resistor in parallel is 
$$\begin{gathered} \frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3} \\ \frac{1}{R_{eq}} =\frac{1}{30}+\frac{1}{30}+\frac{1}{15} \\ {R}_{eq }=\frac{15}{2} \end{gathered}$$

The total current in the circuit is 
$$\begin{gathered} V=IR \\ I =\frac{V}{R_{eq}} \\ I =\frac{10\times 2}{15} \\ I=1.34 A \end{gathered}$$
The potential difference across 30 ohm resistor is 10V.

Regards.