A Riddle a Day -- 78 Logical and Mathematical Puzzles

Intro

Hey! I know this is a bit different from some of the other projects I am working on, but it's something I've considered for a little while.

Every day I will try to post a new riddle along with the answer for the previous day's riddle. Some will be short, some will be long, some will be easier than others, and some will require a little bit of math (just some basic algebra, nothing much).

First to solve each day's riddle accurately (if anyone solves it at all) will receive a shout out in the next day's riddle. You may go to your friends and family for assistance, but only use Google as a last resort (and be honest if you do).

Enjoy!