Question 697140
Solution:

Let x be the number of P1 coins,
y be the number of P5 coins
z be the number of P25c coins.

x+y+z  = 24  ------------eq.1
x = 3+3y     ------------eq.2


put 2 in 1,

3+3y+y+z = 24  = 3+4y+z
4y+z = 21 ---------------eq.4
But z = 1, that is, one 25c coin.
y = 5

x  = 3 +15 = 18

z = 1