What culture invented a mathematical system based on 10 and were able to add and subtract?

Plz me in 1756 george washington was sent on a mission to, a. build a fort at the point where the allegheny and monogahela rivers form the ohio river. b. attack the french at fort duquesne. c. attack the french at fort neccessity. d. deliver a message to the french demanding that they leave the ohio valley.