House numbers along a street consist of two-digit numbers. each house number is made up of nonzero digits, and no digit in a house number is repeated. event a is defined as choosing 6 as the first digit, and event b is defined as choosing a number less than 4 as the second digit. a house number along this street is picked at random, with each number being equally likely and no repeated digits in a number, what is p(a and b) expressed in simplest form?