First number is (x).
Second number is (2x+7).
Third number is (x-12).
Their sum is (x+2x+7+x-12).
x+2x+7+x-12 =131
You can simplify this equation
4x-5=131,
4x=136
x=136/4=34 (first number),
(2x+7)=34*2+7=75 (second number)
34-x=34-12 =22(third number)
Check: 34+75+22=131