Hope you could get an idea from here.
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The answer is 21 + 4x.
You find this answer by adding up all the sides.
9+12+4x= 21+4x ... you don't add 4x because it has a variable that we do not know of the value.
First you find the median, the middle term (if there are an even number of terms it is the average of the middle two terms.) Since you have 21 terms, odd, you just use the middle term, in this case 8. The first quartile works the same way, but just on the left half between the start and the median...so the first quartile is 6.
There are 3.28084 feet in 1 meter.
