please help don't understand

You are studying spark plugs in an automobile engine. One aspect of your investigation is the duration of the "spark burn time" (the duration of the spark) while firing. You test a random sample of 25 spark plugs and obtain the data displayed in the following histogram. Kouanbar 964 976 988 . 1000 1012 1024 1036 Spark Time (microseconds) Use the histogram above to make the following calculations: Mean: Median: Variance: Standard Deviation