There are 60 students in the class and the ratio of girls to boys is m to n. And we need to find the number of girls in the room in terms of m and n.

\(\frac{Girls}{Boys}\) = \(\frac{m}{n}\) = \(\frac{mx}{nx}\) (where x was a common divisor of number of boys and girls)

=> Number of girls = mx and Number of boys = nx
=> Total number of students = girls + boys = mx + nx = 60 (given)
=> x*(m+n) = 60
=> x = \(\frac{60}{m+n}\)

=> Number of Girls = mx = m * \(\frac{60}{m+n}\) = \(\frac{60m}{m+n}\)

So, Answer will be E
Hope it helps!