If both machines are working at once, 200 tshirts (100 in each machine) could be made in 100 minutes, if 200 shirts can be made in machine 1 in 50 minutes, it will take 25 minutes to make 100. machine b takes 150 minutes per each 200, 150 divided by two is 75. 75 + 25 = 100 minutes
It would work better just to use machine one and take 50
minutes, but i dont think thats an answer choice.
edit: i think from the choices your answer would be: 37.5 as if both machines run at once more tshirts can be made