For number one, you can say the some of 10 and quotient of c and five.
For number two you would say the difference of the product of 3 and f and 7.
You can represent the situation for number three this way:
5(7.50 + 2.50x)
The $7.50 plus $2.50x is the cost for one person. Because there are five people, but the five outside of the parentheses that way we understand there are five groups of the entire expression.
