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
