How many two-digit positive integers can be formed from the digits 1, 5, 6, and 8 if no digit is repeated?

Write out all of the 2-digit positive integers formable from 1, 5, 6 and 8, without repetition of digits (e. g., no '22'):

15, 16, 18

Now write out the 2-digit pos. int. that begin with 5: 51, 56, 58.

And so on.

Remember that you can also form 2-dig. pos. int. beginning with 6 and beginning with 8.

Count how many 2-dig. pos. int. you have created. That's your answer.