Harold drives 140 miles in 2.5 hours. If he continues at this rate, how many miles does he drive in 6 hours total?

Calculate for unit rate (1) 
so divide 2.5 by each section 
140/2.5 = 56
2.5/2.5 =  1
56 miles completed in one hour 
so 56 * 6 = 336
336 miles are completed in 6 hours