log2 36=a
log2 6^2=a
2log2 2*3 =a
log2 2 +log 2 3=a/2
1+log2 3=a/2
log2 3 =a/2-1
log2 10=b
log2 2*5=b
log2 2 + log2 5=b
log2 5=b-1
log2 15=log2 3*5=log2 3 + log2 5
=a/2-1+b-1
=a/2+b-2