Solving a literal equation

If r = 3s + 1 and t = s - 4, then what is r in terms of t?

r = 3s + 1
t = s - 4 ---------> s = t + 4   {added 4 to each side}

r = 3(t + 4) + 1   {substituted (t + 4), in for s, into top equation}
r = 3t + 12 + 1   {used distributive property}
r = 3t + 13   {combined like terms}

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