Answer:
51cm is the answer.
Step-by-step explanation:
a = ?
b = 68cm
c = 85cm
According to the Pythagoras theorem,
a² + b² = c²
a² + 68² = 85²
a² + 4624 = 7225
a² = 7225 - 4624
a² = 2601
a = 51cm
∴ the porch is 51cm tall.
