let k the number of tickets sold to kids and a the number of tickets sold to adults. then it will be; k+a = 200 (1) and 2k + 3a = 475 (2) from the (1) we get k=200-a plugging this value of k to (2) we get
2(200-a)+3a = 475 --->>> 400-2a+3a=475 --->>>> a=475-400 --->>> a=75 so number of adults = 75
(and number of kids = 200-75=125)