Question 289499
This problem involves knowing how to set up the algebraic expression, given the English.
$1986 is the total amount of money spent.
50 is the total amount of units bought.
So if we let (50-x) represent the amount of Scientific Calculators,
then x represents the amount of graphing calculators. STOP--
Go over what I just meant. Understand this!

OK? Now 9(50-x) represents the amount of money spent on Scientific Calculators.
(I've decided not to deal with dollar signs right now.)
57(x) represents the amount of money spent on Graphing Calculators.
NOW...9(50-x) + 57(x) = 1986.
We use the Distributive Property of Multiplication over addition and subtraction...
450-9x+57x=1986
48x=1536
x=32
NOW we go back and read what the problem is asking for. And, we want to remind ourselves what x was/is. x is the amount of Graphing Calculators, which is 32. (50-x) is the amount of Scientific Calculators, which is then 18.