Plz help

I got the first 2 but not the last one

Whats are the trickiest steps to do when adding or subtracting rational expressions? how does knowledge of rational numbers u in adding and subtracting rational expressions?

Rob filled 5 fewer plastic boxes with football cards than basketball cards. he filled 11 boxes with basketball cards.

Agroup of three friends order a combo meal which includes two slices of pizza and a drink each drink is priced at $2.50 the combined total of $31.50 how much is the cost of a slice of pizza