What is the first quartile of the data set? {51, 42, 46, 53, 66, 70, 90, 70} a-48.5 b-59.5 c-61 d-80

The first quartile is the middle of the lower half of the data.

To find this you must:
1.  Order the data from least to greatest. 
   42, 46, 51, 53, |  66, 70, 70, 90
2. Next, find where the middle of the data set it - see the line above
3.  Look at the lower half of the data - see the bold half above.
4.  Find the middle of that half - see the underlined numbers above.
5.  Find the middle of the 2 numbers
    (46 + 51)
           2      =  48.5

48.5 is the 1st quartile.

It is just law about 2 parallel lines. that x=180-47=133. And EBC=47°