Section 234F fees is liable to interest under section 234A

when we calculate the Interest under S234A for late return filing in that case we have to calculate it on tax amount or on tax plus fees u/s234F
for eg-
tax amount -50000
234F fees- 5000
than interest will be on-
a) 50000 or
b) 55000
I referred Vinod Gupta sir book he is calculating on 55000 but I am doubtful about that
so can u please suggest me what should I do in exam?