How do i calculate the first quartile and the third quartile???

The Median: 78, The First Quartile: 63, and The Third Quartile: 99

Step-by-step explanation: Ok, so let's put the data set from least to greatest

(63, 63, 76,) (77, 79,) (84, 99, 99)

First Quartile              Third Quartile

First, let's find the median, since you made a little mistake...

77 + 79 = 156

156 ÷ 2 = 78

The median is 78!

Now, let's determine the first quartile and the third quartile.

For the the first quartile/third quartile it'll be the middle number, if it's even we'll do the same extra step just like we'll do for the median. In this case it's not even therefore...

First Quartile: 63

Third Quartile: 99

I hope this helps!