Hey!
-----------------------------
Question 16:
6 - x = 10
6 + (-x) = 10
6 + (-x) -6 = 10 - 6
-x = 4
-x/-1 = 4/-1
x = -4
-----------------------------
Question 17:
4x + 3 = 9
4x + 3 - 3 = 9 - 3
4x = 6
4x/4 = 6/4
x = 1 1/2
-----------------------------
Hope this helped, good luck!