Question 309710
child's plate = c
adult's plate = a


(1) c + a = 250
(2) 3.5c + 7a = 1347.50
multiply equation (1) by 7
(1) 7c + 7a = 1750
(2)3.5c+ 7a = 1347.50
---------------------- (-)
3.5c = 402.5
c = 402.5/3.5 = 4025/35 = 115


c + a = 250
115 + a = 250
a = 250 - 115 = 135


so, child's plates reserved = 115 plates
adult's plate reserved = 135 plates