Perimeter is all the lengths of the sides added together, that is, t+(t+3)+t+(t+3).
For the second equation, I’m guess you simplify the first:
Without the brackets, t+(t+3)+t+(t+3) = t+t+t+t+3+3 = 4t+3+3
Simplify = 4t+6
Therefore, first equation = t+(t+3)+t+(t+3), second equation = 4t+6