This kind of a problem needs to be done with system of equations.
First, identify your variables.
x = larger number
y = smaller number
Next, set up your equation.
x+y=35
3x=4y
Now, solve your system of equation through substitution.
x+y=35
3x=4y
_____
x+y=35
x=4y/3
4y/3 +y = 35
7y/3=35
7y=105
y=15
Then, solve for x.
3x=4y
3x=4(15)
3x=60
x=20
So, the larger number is 20 and the smaller number is 15.
HOPE THIS HELPS:)