How many 4-digit numbers divisible by 5, all of the digits of which are even, are there?

100

Step-by-step explanation:

If a number is divisible by 5, then the last digit is either 0 or 5.

Since all the digits are even, the last digit must be 0.

There are 4 options for the first digit (2, 4, 6, 8).

There are 5 options for the second digit (0, 2, 4, 6, 8).

There are 5 options for the third digit (0, 2, 4, 6, 8).

So the total number of numbers is:

4×5×5×1 = 100

you can't solve x because it is 2 linear equation and you only have one equation