Question 971925
joint variability
4 trucks*5 hours cost $1500.  It is 20 truck-hrs. or $75 (1500/20) per truck-hr.

10 trucks *11 hours is 110 truck-hrs.  The cost would be $75 * 110=$8250.

It is 2.5 times the number of trucks and 2.2 times the number of hours.
Joint variability is multiplying by both, which is here 2.5*2.2=5.5 

$1500*5.5=$8250.