Answer:
30$
Explanation:
lets assume you didn't have a coupon then the total bill would have been 120$
so for 4 friends including u the bill would have been 120$
: 4 friends = 120 $
for : 1 friend = x$
cross multiply
4x = 120 × 1
4x =120
divide both sides by the coefficient of x
x =120 \ 4
x = 30$
therefore: 1 friend = 30$