Dana bikes 10 miles in 50 minutes at this rate how far can she bike in 90 minutes

There r 2 ways to do this...

(1) unit rate...
      10/50 = 1/5 miles per minute
     In 90 minutes1/5 * 90 = 90/5 = 18 miles

(2) proportion..
      10/50 = x/9010 miles to 50 min = x miles to 90 min
       cross multiply
       (50)(x) = (10)(90)
        50x = 900
        x = 900/50
        x = 18 minutes.