City L and City M are 558 km apart. At 5.51 p.m., Bobby is travelling at a uniform speed left City L for City M while Justin set off from City M to City L along the same road at a uniform speed, which was 6 km/h slower than that of Bobby. The two met at 8.51 p.m.

1. Find the speed of Bobby.
2. If Justin continued to travel at the same speed, how long would it take for him to reach his destination after the two met? Express your answer in mixed number.

(a)
Time taken for Bobby and Justin to travel from 5.51 p.m. to 8.51 p.m. = 3 h

Average speed of Bobby and Justin
= 558 ÷ 3
= 186 km/h

Bobby's speed
= (186 + 6) ÷ 2
= 192 ÷ 2 
= 96 km/h

(b)
Justin's speed
= 96 - 6
= 90 km/h

Distance that Justin travelled in 3 h
= 3 x 90
= 270 km

Remaining distance that Justin needed to travel
= 558 - 270
= 288 km

Time that Justin needed to reach his destination after the two met
= 288 ÷ 90
= 3¹⁸₉₀
= 3¹₅ h

Answer(s): (a) 96 km/h; (b) 3¹₅ h