Answer:
156 seats
Step-by-step explanation:
since you are adding 8 seats for each row you go up on, it will be 28 for the 4th row, 36 for the 5th, 44 for the 6th, 52 for the 7th, 60 for the 8th, 68 for the 9th, 76 for the 10th, 84 for the 11th, 92 for the 12th, 100 for the 13th, 108 for the 14th, 116 for the 15th, 124 for the 16th, 132 for the 17th, 140 for the 18th, 148 for the 19th, and 156 for the 20th.