Answer: 154
Step-by-step explanation:
The mean is calculated by adding up all the numbers and dividing by the number of observations added up.
The above can therefore be expressed as:
(88 + 55 + 99 + x) / 4 = 99
242 + x = 99 * 4
242 + x = 396
x = 396 - 242
x = 154
