\[25z^{2} - (2t + 3z)^{2} =\]
\[= (5z - 2t - 3z)(5z + 2t + 3z) =\]
\[= (2z - 2t)(8z + 2t) =\]
\[= 2 \cdot 2(z - t)(4z + t) =\]
\[= 4(z - t)(4z + t).\]