Let’s call the angles ##3x,4x and 5x##
They must add up to ##180^o## in a triangle, so:
##3x+4x+5x=12x=180->x=180//12=15##
So the angles are: ##3*15=45^o## ##4*15=60^o## ##5*15=75^o##
Check answer: ##45+60+75=180##
Let’s call the angles ##3x,4x and 5x##
They must add up to ##180^o## in a triangle, so:
##3x+4x+5x=12x=180->x=180//12=15##
So the angles are: ##3*15=45^o## ##4*15=60^o## ##5*15=75^o##
Check answer: ##45+60+75=180##