Math
posted by Sunny .
A girl earns $6.00 an hour when she works Monday through Friday and $9.00 an hour on Saturday. Last week, her salary was $273 for 42 hours of work. How many hours did she work on Saturday?

first, represent unknowns with variables:
let x = number of hours she worked for mondayfriday
let y = number of hours she worked for saturday
set up equation according to conditions given:
(1) x + y = 42
(2) 6x + 9y = 273
there are many ways to solve for this,, if we use substitution method,,
choose an equation (in this case, equation (1)), then express one of the variables in terms of the other,, thus we express x in terms of y:
x + y = 42
x = 42  y
now we substitute this to equation (2):
6x + 9y = 273
6(42y) + 9y = 273
now you solve for y.