The total amount raised is the sum of the amounts raised by the car wash and the dinner. The car wash raised 7c - 18. The dinner raised 6s - 45. We now add the expressions and combine like terms.
7c - 18 + 6s - 45
We need to combine like terms. Like terms are terms that have the same variables and the same exponents on the variables. 7c and 6s are not like terms since c and s are different variables. They cannot be combined together. Plain numbers, like -18 and -45 are lime terms because their variable parts are the same; they both have no variables.
