Answer:
12 50p coins were collected
Explanation:
Let x represent the number of 50p coins. Then 39-x is the number of 20p coins. The total value of coins collected was ...
20(39-x) +50(x) = 1140
780 +30x = 1140 . . . . . . . simplify
30x = 360 . . . . . . . . subtract 780
x = 12 . . . . . . . . . divide by 30
12 of the 50p coins were collected.
__
39 -12 = 27 of the 20p coins were collected.