Answer:
12.) b = (2S/n) - a
13.) x = 1000 - 20y
Explanation:
12.) *goal is to isolate b
S = n/2 (a + b)
S(2/n) = a + b
**multiply both sides by 2/n to get rid of n/2
(2S/n) - a= b
***subtract a from both sides to leave b alone on one side
13.) *goal is to isolate x
0.30x + 6y = 300
0.30x = 300 - 6y
** subtract 6y from both sides
x = (300 - 6y)/ 0.30
*** divide 0.30 from both sides to leave x bu itself
x = 1000 - 20y or -20y +1000
****300 ÷ 0.30 = 1000
-6 ÷ 0.30 = -20
Done!