st + 3t = 6 for s
Subtract 3t to both sides
st + 3t - 3t = 6 - 3t
Simplify
st = 6 - 3t
Divide both sides by t
st/t = (6-3t)/3
simplify
s = 6/3 - 3t/3
s = 2 - t
C=2pir, so take half of 15 which is 7.5 and plug it in as r and you get 47.12. Or just look up circumference calculator on google.
