This demo takes some thought so you may want to watch it a few times to fully understand. Writing the expression and then we simplify it so that it is more usable in future.
This shows how to represent the two unknowns using their given relationship so that a linear equation can be written using one variable. Then that equation is solved to answer the question
Talks about how to interpret the words to create two equations, then solves them together using the elimination method, making opposites of one variable's terms sot that the equations can be…