ok, so 2 solutions, 1 is if buy cards for every guest
other is if buy only 1 gift card
1st one
63.9=5.4x+11.7x
63.9=17.1x
divide both sides by 17.1
crazydecimal=x
wrong, yo can't buy a decimal amount of cads
2nd
63.9=5.4+11.7x
minus 5.4 both sides
59.5=11.7x
divide both sides by 11.7
5=x
5 guests
B is answer