The digits 3,4,5,6,7,and 8 are randomly arranged to form a 3 digit number not repeating. find the probability that the number is even and greater than 800.

I'm at a bookstore with $\$35$ in my pocket and a $20\%$-off coupon. what is the cost of the most expensive book i can buy with my money and the coupon? (assume that there are books of every possible price in the bookstore. it's a large bookstore! )