Here are three problems from class on Wednesday, 15 March.
The first two are investment problems. Set up the table (like we did back in 055) with I=PRT along the top and a row for each investment and the total. Fill in what you know. Make sure that you make x the thing you need to find. Set up an equation based on a relationship you know, and solve for x.
This problem could be solved as a three-variable system of linear equations, but it is probably easier to do it the way I did it here: write down the relationships among the variables, substitute to get everything in terms of one of the variables, and then substitute all of the expressions in terms of that variable into the equation that links them all together. Solve that equation, and then substitute the solution into the other relationships to find the values of the other variables.