Answer:
The tip was 7.77 dollars, which represent 18.5% of the value of the bill
Step-by-step explanation:
Dollars paid as tip
$49.77 - $42 = $7.77
$42 represent 100% of the bill
$7.77 ---------------x
x = (7.77/42)*100% = 18.5%
30
-12 + 30 = 18