A Go first 40* 1/2=20.
170-20= 150 left.
The express train took 20 minutes to repair the car, and B left 30* 1/3= 10.
The remaining150-10 =140.
When Party A stops for maintenance, it will be (X+ 1/3) hours after the delay of X hours.
Set the local train to leave for (X+ 1/3) hours and meet the express train.
Equation: 40x+30 (x+1/3) =170-40 *1/2.
X=2
X+ 1/3=7/3 hours = 140 minutes.