There are two class rooms A and B. If 10 students are sent from A to B, the number of students in each room is the same. If 20 students are sent from B to A, the number of students in A is double the number of students in B. then the number of students in each room is ________

Question

$(a) \;A=100;B=80 \\(b)\;A=80;B=100 \\(c)\; A=90;B=90 \\(d)\;A=70;B=110$