Part a
power = 3.9 \times {10}^{33} erg \: {sec}^{ - 1}
energy \: in \: 3.25 \times {10}^{3} sec = 3.9 \times {10}^{33} \times 3.25 \times {10}^{3} = 12.675 \times {10}^{36}
part b
1.435 . 10^3 mm = 1.4m
1.435 . 10^-3 mm = 0.001435m
so the first one ie 1.4m is more reasonable as tge second one is too small quantity.
Hope it helps.