Switch to using expr() function and make more interesting prpblem
Fix solution entry box and make better range of problems
Write function to simplyify terms in sum of expressions
Split into separate + and - exercises to make it easier to deal with hints
Change method of generating problem to avoid questions that simplify
Simplify fraction where required
Add solution
Remove unnecessary variables
Avoid the rare chance that the two constants could be 0 and the coefficients share a factor
Change var to div
Merge pull request #43440 from petercollingridge/rational-expr

Adding and subtracting rational expressions 1