Answer
$(A^t)^t=A$
Work Step by Step
We can write the matrix $A$ as $[a_{ij}]$ where $a_{ij}$ represents the element in the ith row and jth column of $A$.
The transposed matrix interchanges the rows and columns of the initial matrix.
$(A^t)^t=([a_{ij}]^t)^t =[a_{ji}]^t=[a_{ij}]=A$$