0.411 times 0.411 times 0.411 times 0.411 times 0.411 (for the 5 flips that do not land on heads) times 0.599 (for the time that it does land on heads).
You need to set it up as a fraction and make the fractions equal each other. 2/3 (2 of their books for 3 of yours) x/18 (x amount of their books for 18 of yours) (2/3)=(x/18) multiply both sides by 18 and you get 36/3 which reduces to 12
