Casualty medical officer in a hospital has received four requests for ambulance van facility. Currently six vans are available for assignment. The estimated response time is given in the table. Determine which vans should respond the four requests and what will be response time?

Van

Incident

$1$

$2$

$3$

$4$

$5$

$6$

I

$15$

$13$

$15$

$18$

$16$

$14$

II

$16$

$12$

$17$

$16$

$18$

$13$

III

$14$

$17$

$15$

$15$

$14$

$16$

IV

$17$

$19$

$14$

$17$

$13$

$18$