For what value of m will the system of equations 18x - 72y + 13 = 0 and 7x - my - 17 = 0 have no solution?

Answer: Option A

18x - 72y + 13 = 0
7x - my - 17 = 0
There is no solution, means they are parallel
$$\begin{array}{rl}& \frac{a_1}{a_2}=\frac{b_1}{b_2}\\ & \Rightarrow \frac{18}{7}=\frac{72}{m}\\ & \Rightarrow m=7\times 4\\ & \Rightarrow m=28\end{array}$$