damn...i used Oksanav's advice and here's where I am stuck
x= 1/2 (25,000m/3,600s + 65,000m/3,600s)(8.5s)
x= 1/2 (90,000m/7,200s) (8.5s)
now here's where I am gettin stuck...im multiplying (90,000m/7,200s) by (8.5s) and getting 106.25 and then taking half of that because of the '1/2'...