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
Substitution.
Elimination.
Using a Combination of methods.
Using absolute value
I hope this helps!