they're similar, so each length will be divisible by the same number
DF is 24 cm
AC is 16 cm
24/16 = 1.5
this means that you would be able to multiply each number on the smaller triangle by 1.5 or divide each number on the bigger triangle by 1.5 to get the number of the other triangle
since BA is 12 cm
ED will be 12 * 1.5
12 * 1.5 = 18
ED is 18 cm, which is B