Answer :
they can ride their bike 12 miles because in 6 minutes they ride 0.8 miles so in 1.5 hours they ride 12 miles. 0.8 * 10 = 8 miles 1 hour so 0.8 * 5 = 4 miles 0.5 hours 8 miles + 4 miles =12 miles 1 hour + 0.5 hours = 1.5 hours