So Car A = 871/8.9 = 97.86sec

Car B = 871/5.1 = 170.78 sec

Hence their distance is 170.78-97.86 = 72.92 about 73 sec depending on how the numbers are rounded off.

Second of all, this problem makes no sense and is unsolvable. 73 seconds is a time unit, not a distance unit. They are 73 seconds apart according to what speed, car 1 or car 2? This problem needs more info.

5.1×73=372.3 km

now, you can figure the distances as follows

8.9x=5.1x+372.3

3.8x=372.3

x=97.97 km, rounded off

see if it is true

8.9x=5.1x+372.3

8.9(97.97)=5.1(97.97)+372.3

871.9=499.6+372.3

871.9km=871.9km

You had it right, just round off, or keep all decimals, as needed or you feel best.

73=871.965/8.9 – 871.965/5.1

73=97.97359 – 170.97353

73=-72.99994

If you want an answer with a positive number just put the factor with the lower denominator first.