solve the equation: with Logarithm & one word problem

the stress i had a few days has went down so much since i became a member here, i actually feel prepared for my test coming up thanks to all of you. out of the 45 problems these are the last few im having serious problems with, i wish i understood these instead of bugging you guys haha

these last 4 problems i cant get a single answer.. problems #20 #21 and #22

problems #24 is a word problem that i cant figure out as well, help with any problems will be much appreciated.

i scanned the packet, here are the few problems im having trouble with.

the test is friday and i want to know the material as best as possible because the last test i failed. i normal dont fail things, its just harder for me to understand math more than others. its very frustrating :(