Answer:
Let's say the number of boys is X and the number of girls is Y.
Then we have 35 students in the class, this means X+Y=35
The ratio of boys to girls is 3:4, so if we multiply the number of girls (Y) in the class by 3 and the number of boys (X) by 4 they should be equal 4x=3y
Now we have 2 with 2 variables
Let's multiply the first equation by 4, 4x+4y=140
Now replace the 4x with 3y, 7y=140
So we have 20 girls in the class (y=20) and 15 boys (20+15=35)
The answer is: we have 5 more girls in the class
