This is sort of simple but the drawing isnt that clearly drawn.
If the resistors are: 5,10,20,25 ohms, and the source is 9v and 1.8 amps,
then the person who did the original analysis did not do it correctly.
Isc is not equal to V2/10, it is equal to (V2-9)/10, which is 300ma.
They forgot to subtract the 9v from V2 before calculating the current.
Tell them to check their result.
It looks like you may need to check your result also.
The real problem however is that they use the notation "Isc" for both the
top and bottom loops, where the bottom loop is actually what they calculated:
but the top loop is 0.3 amps.
So ask them which Isc they want to know. Apparently it is the bottom loop.