Each month, Kaisorn deposits 50 point 00 dollars onto her public transportation card. It costs her 2 point 50 dollars per trip to ride the subway. Thom deposits 40 point 00 dollars on his public transportation card. It costs him 2 point 00 dollars per trip to ride the subway. If x represents the number of trips and y represents the amount remaining in each account, which system of equations represents their transportation costs?