Help! due august 12th

The output of the first one is 21 and you need to find x to the power of 2 subtract 4. So to find where we started add 4 to 21. This gets you to 25 and the square root of 25 is 5. So for the first one X=5

Work showed:

Y=x^2-4
21=x^2-4
Add 4 to both sides
25=x^2
Find the square root of 25 to get X as 5

For the second output (y), plug 21 for x

Y=4x+6
Y=4(21)+6
Y=84+6
Y=90

First part: X=5
Second part: Y=90

Element 17 is chlorine it is a group 7 element(halogen) and belongs to period 3 of the periodic table