This is another application of simultaneous equations.

let the number of reserved tickets sold be r

let the number of general admission tickets sold be g

then the the money gained from selling reserved tickets is 7r and the money gained from selling general admission tickets is 4g. the total number of tickets sold is 450. so we have:

r + g = 450 ..................(1)

7r + 4g = 2775 .............(2)

4r + 4g = 1800 ..............(3) = (1)*4

7r + 4g = 2775 ..............(2)

3r = 975 .......................(4) = (2) - (3)

=> r = 975/3

=> r = 325

but r + g = 450

=> 325 + g = 450

=> g = 450 - 325

=> g = 125

so 325 reserved tickets were sold and 125 general admission tickets were sold