Question 561644
Bus 1------- speed =x--------------9.30
Bus 2 -----speed = x+6--------------10.00

Before Bus II starts Bus I has traveled 1/2*x

so distance between them when bus II starts = (312-(1/2)x)

=(624-x)/2

their combined speed = x+x+6=2x+6

t= d/r

they cross at 12
so 2 hours = t

2=(624-x)/2)/(2x+6)
2= (624-x)/2(2x+6)
4(2x+6)=624-x
8x+24=624-x
9x=600
/9
x=600/9
x=66.66 mph

Bus I speed = 66.66 mph
Bus II speed = 66.66 +6 = 72.66 mph