This book teaches how to set up a math problem, not how to do the math. I need help with the math on the last page next to the red arrow. v=x/t. The missing values in this physics problem are circled. If x and t are missing, how is it possible to get v? It is my understanding that I choose the equation that has only one missing value, rearrange the equation and solve for that missing value. But in this case there are too many missing values.