Adding and subtracting algebraic fractions is a similar process to adding and subtracting normal fractions. The denominators of each fraction are different, \(3t\) and \(7t\), so a common denominator ...

Parsing algebraic expressions is always a pain. If you need to compute, say, 2+4*2, the answer should be the same as (2 + (4 *2)), not ((2 + 4) * 2) — in other words, the right answer is 10, not 12.