Express the following as a single logarithm:
1. log [3] 7 + log [3] 5

2. log [2] 16 + 3log [2] 4 - log [2] 8
3log [5] 9 + log [5] 2
4. log [5] 5 + log [5] 10 - log [5] 3 = 0
3.
4.