Why x is (i+1)*(j+1) ? why not i*j ? i didn't get part

#1

Why x is (i+1)(j+1) ? why not ij ? i didn’t get part .

#2

i and j are related to index…so they start from 0.
We do (i+1) x (j+1) because we consider total elements.
Consider when i=0 and j=0… then i x j would give 0.