so the ratio of boys-who-tried to boys-who-made-it=40:16
40:16 simplifies to 10:4 or 5:2
so if 12 girls were selected and we want to find an equal ratio, then we want to find the ammount of girls that tried out if the ratio is the same as the boys (5:2)
if 12=2 units then 1 unit=6
5 units times 6=30
the equivilent would be 30 girls tried out and 12 made it