here we have a system of 2 equations with two uknowns.
(1) 3c + 6i = 1230
(2) 2c + 2i = 620 where c = cost for cub ticket. and i = cost for indian ticket
subtracting the (2) from (1) we get. (3) c + 4i = 610. so c =610 - 4i substituting where c = 610-4i
we get i = 100. substituting i = 100 we get c = 210