You drive 6.0 km at 50 km/h and then another 6.0 km at 90 km/h. your average speed over the 12 km drive will be

V1=50km/h
v2=90km/h
s1=s2=6km
s=12km

The average speed over the 12 km drive:
v=s/t

The time needed to drive 12km will be:
t = t1+t2

t1=s1/v1, t2=s2/v2

t=s1/v1+s2/v2=(s1v2+s2v1)/(v1v2)

v=sv1v2/(s1v2+s2v1)=12*50*90/(6*50+6*90)=64,28 km/h

$250 deductible means jane must pay the first $250 of her bill. so the insurance company paid = (80% of bill) - deductible = (0.8 x $2550) - $250 = $2040 - $250 = $1790 and jane's cost is = (bill) - (insurance payment) = $2550 - $1790 = $760