Answer:
18
Explanation:
Let number of girls be 'x'.
So, Number of boys = Number of girls - 4
= x - 4
Total number of students in a class = 40
Number of girls + Number of boys = Total number of students in a class
x + x - 4 = 40
2x - 4 = 40
2x - 4 + 4 = 40 + 4
2x = 44
x = 22
Number of boys = 22 - 4
= 18