I am late to the party but just thought that I would add this to make it abundantly clear how easy this stuff is. Just go to
https://en.wikipedia.org/wiki/Lorentz_transformation#Proper_transformations to get the Lorentz transform matrix. For ##v=(c/2,0,0)## we get$$\Lambda =
\left(
\begin{array}{cccc}
\frac{2}{\sqrt{3}} & \frac{1}{\sqrt{3}} & 0 & 0 \\
\frac{1}{\sqrt{3}} & \frac{2}{\sqrt{3}} & 0 & 0 \\
0 & 0 & 1 & 0 \\
0 & 0 & 0 & 1 \\
\end{array}
\right)$$ Then we simply use that transformation matrix to determine events ##(ct,x,y,z)## in the ground frame. $$\Lambda \cdot \left(0,0,0,0\right)=\left(0,0,0,0\right)$$$$\Lambda \cdot \left(\frac{c}{2} ,\frac{c}{2} ,0 ,0 \right) = \left( \frac{\sqrt{3}c}{2},\frac{\sqrt{3}c}{2},0,0 \right)$$$$\Lambda \cdot \left(1 c ,0 ,0 ,0 \right) = \left(\frac{2 c}{\sqrt{3}},\frac{c}{\sqrt{3}},0,0 \right)$$ You can do the subtraction and evaluate the numbers to see that the time is 0.87 for the forward and 0.29 for the reverse.
As long as they can do matrix multiplication, it is indeed high school level. The reluctance to do this for the lazy alien was due to our usual approach of encouraging the OP to learn for themselves, not because this was in any way challenging to do
