1 adult + 2 kids: admission = 8.75

2 adults + 5 kids: adm = 19.75

I have the answer, just need the formula - I guessed and checked (a lot) and got kids' tickets = 2.25
adults' tickets = 4.25

2 answers

a + 2k = 875 (1)
2a + 5k = 1975 (2)

from (1) a = 875-2k
sub into (2)
2(875-2k) + 5k = 1975
1750 - 4k + 5k = 1975
k = 225
then a = 875-450
a = 425
thanks