Question 693263
In the number 21, the tens digit 2 is twice the units digit 1.
In the number 42, the tens digit 4 is twice the units digit 2.
In the number 63, the tens digit 6 is twice the units digit 3.
In the number 84, the tens digit 8 is twice the units digit 4.

Gosh that was really hard, wasn't it?  Can you count them?