Answer:
s = 6
Explanation:
Goal is to isolate the variable (s)
1/2s = 4s - 21
Subtract 4s from both sides - this cancels out the 4s on the right side and moves it to the left side
1/2s - 4s = -21
To add or subtract fractions, they must have a common denominator
Convert 4s to a fraction over 2
1/2s - 8/2s = -21
Subtract the numerators and keep the denominators
-7/2s = -21
Remember the goal is to isolate the variable
In order to get rid of the -7/2, we multiply by its reciprocal (which is -2/7)
What we do to one side, we must do to the other (this means multiply by -2/7 on both sides
-7/2s × -2/7 = -21 × -2/7
s = -21 × -2/7
Negative × negative = positive
s = 42/7
Divide 42 by 7
s = 6