When we have 2 equations in 2 variables, and one of the equations has y written in terms of x, then we can use the substitution method to solve the equations. Simply take the equation with y isolated, and substitute it into the second equation where we have y. This will give us one equation with only the variable x. Solve it for x. Then take the x value and plug it into the other equation to find y.
Once I modeled one of these equations, Rory was able to work out the rest of them with minimal errors. He understands the concept and process.