There are no real solutions
x = 32
To find the media, you take the middle number. If there is no discrete middle number, take the sum of the two closest to the middle and divide by 2.
(24 + x)/2 = 28
Multiply by 2 on both sides to get:
24 + x = 56
Subtract 24 from both sides to isolate the variable:
x = 56 - 24
x = 32
As the key suggests, the left part is the integer part of the number, while the digit on the right is the decimal part of the number.
So, for example, the first row describes the two values 97.2 and 97.8, while the second row describes the values 98.1, 98.3 (repeated twice), 98.5, 98.6 and 98.7 (repeater three times).
So, the number of values is given by the number of leaves: you simply have to count how many digits are there on the right part of the screen.
The answer is thus 24