(a) loga(ab)=logaa + logab
= 1 + logab
= 1 + logbb/logba
= 1 + 1/3.75
= 19/15
(b) logb(a/c)=logba - logbc
=3.75 - 1.25
=2.5
(c) Did you mean logb(ac)2 ?
If so, then
logb(ac)2=2logbac
=2(logba + logbc)
=2(3.75 + 1.25)
=2 x 5
=10
(d) logca=logba/logbc
=3.75/1.25
=3