Please help it will be brainlist

What are “like terms”? why can we only add like terms?

3questions show how you solved the problem 1. subtract & simplify (–y2 – 4y – 8) – (–4y2 – 6y + 3) 2.multiply and simplify 2x2y3z2 · 4xy4x2 3.multiply and simplify (x – 4) (x2 – 5x – 6)

The students at jefferson middle school are raising money for a charity by selling t-shirts and hats. the number of t-shirts sold was 3 times the number of hats. the profit was $5 for each t-shirt sold and $2.50 for each hat sold. the students raised $840 for the charity. they used the system below to analyze their success and found the solution to be (144, 48). 5x+2.50y=840 x=3y how much did they earn from t-shirt sales?