143
because the equation would be 11x+x=156. so if you add like terms it would be 12x=156. then 156/12 is 13. 13 is how many miles Early biked.
so dory biked 11 times as many miles, so you would solve 13(Early's miles) times 11(Dory's miles). 13x11=143
so dory biked 143 miles last month
