Christine buys 7 hamburgers and 3 sodas for $27.95. laura buys 5 hamburgers and 4 sodas for $23.40. how much does a hamburger cost?
a. 1 .85
b. $3.20
c. $6.80
d. $6.55
e. $3.50

7h+3s=27.95 subtract 7h from both sides

3s=27.95-7h  divide both sides by 3

s=(27.95-7h)/3

Then we are told:

5h+4s=23.4,  using s found above makes this equation become:

5h+4(27.95-7h)/3=23.4  multiply both sides by 3

15h+4(27.95-7h=70.2  perform indicated multiplication on left side

15h+111.8-28h=70.2 combine like terms on left side

-13h+111.8=70.2 subtract 111.8 from both sides

-13h=-41.6  divide both sides by -13

h=$3.20