Answer:
D. 50 students
Explanation:
First we find the area of the classroom which is worked out below and it is the shape of a rectangle;
Area of a rectangle = Length * Breadth
 = 60 ft * 40 ft
 = 2400 ft²
Now to find the number of students that she will allow in the classroom, we have to divide the area of the classroom which is 2400 ft²by the amount of space allocated to each student which will be;
= 

= 50
This means she will allow 50 students into her class.