What’s the answer I don’t understand it

Answer:
40 boys
Step-by-step explanation:
Set b equal to total number of boys and g total number of girls.
From the ratio we have the following equation:
g/b=5/8
Cross multiply:
8g=5b
We also know the total number of students is 65.
So: g+b=65
Thus, here is our system of equations:
8g=5b
g+b=65
Using the 1st equation, set it equal to girls in terms of boys.
g=(5/8)b
Substitute g in second equation:
(5/8)b+b=65
Simplify
(13/8)b=65
13b=520
b=40
Thus, we know there are 40 boys and 25 girls.