Question 107193
3*X+3(X+80)=2940
3X+3X+240=2940
6X=2940-240
6X=2700
X=2700/6
X=450 MPH FOR THE SLOW PLANE
450+80=530 MPH FOR THE FASTER PLANE.
PROOF
3*450+3*530=2940
1350+1590=2940
2940=2940