Answer: There are 69 adults and 72 children went to the concert.
Step-by-step explanation:
Let x be the number of adults, and y be the number of children.
x + y = 141
3.5x + 2.5y = 421.5
x + y =141
x = 141 - y
3.5(141 - y) + 2.5y = 421.5
493.5 - 3.5y + 2.5y = 421.5
493.5 - y = 421.5
-y = -72
y = 72
x + y = 141
x + 72 = 141
x = 69
