solve the equation for the bold variable

The answer to problem 14 is the equation c = 3i/e
To get this answer, you multiply both sides by 3 to undo the division of 3. Also, you divide both sides by 'e' to undo the multiplication of 'e'.
So it would look something like this
i = ec/3
3*i = 3*ec/3 ... multiply both sides by 3
3*i = ec
ec = 3i
ec/e = 3i/e ... divide both sides by e
c = 3i/e
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Problem 15)
P = 2L + 2W
2L + 2W = P
2L + 2W-2L = P-2L ... subtract 2L from both sides
2W = P-2L
2W/2 = (P-2L)/2 ... divide both sides by 2
W = (P-2L)/2
So the final answer is W = (P-2L)/2