Question 145947
Let x = phone cost
Let y = water cost
:
Write an equation for each statement:
"Phone and water bills together cost a company $790 for December."
x + y = 790
:
" If the phone cost four times as much as the water,"
x = 4y
:
how much was each utility?
:
Using the 1st equation; x + y = 790,  substitute 4y for x
4y + y = 790
5y = 790
y = {{{790/5}}}
y = $158 is the water bill
:
Using x = 4y, substitute 158 for y
x = 4(158)
x = $632 is the phone bill
:
:
Check 158 + 632 = 790; confirms our solutions