video explanation

text explanation

to find the average (arithmetic mean) of all 10 test scores, we need to find the sum of all 10 test scores, and divide that by 10:

the question tells us that the average is 62: 

to find the sum of all 10 scores, we need to add the following numbers (based on the information in the frequency table): 

now, we can solve this for x. first, we'll multiply both sides by 10, and then we'll simplify the right hand side: 

so the answer is b. (note that for the last step, we divided both sides by 4.)