The sum of the sides of a triangle is equal to 180º.
The three angles will be: 3x,4x and 5x.
we can suggest the following equation:
3x+4x+5x=180
12x=180
x=180/12
x=15
The angles would be:
3x=3(15)=45
4x=4(15)=60
5x=5(15)=75
Answer: the highest angle would measure 75º.