Solving Linear Systems with Substitution - Definition & Examples

One day, I visited the new bike garage that was installed for my apartment complex. I was curious to see how many bicycles there were compared to tricycles, but I couldn't see into the building. All I knew was that there were more bicycles than tricycles.

Motivated by this curiosity, I kneeled down to count the total number of wheels, and counted a total of $51$ wheels. I also spotted a digital sign at the entrance that said, "$8$ out of $30$ bike spaces avalible."