A combination lock has some identical cylindrical tumblers each with the digits from 0-9 inclusive printed on each of the cylinders. The cylinders are aligned on a common axis. Each cylinder can be spun so that only one digit is visible on each cylinder. The digits, when read from left to right, form an integer. However, for these problems, we will allow an integer to start with a 0, such as 0123. If the displayed number is the correct combination, the lock can be opened. Use the clues to open each of the following locks. The first lock has two cylinders.

The sum of the tens digit and ones digit is 9.

The tens digit is less than the ones digit.

The ones digit is a square number.

What is the two-digit number that opens this lock?