Explanation:
that is a large gift. wow ! you have a lucky teacher ...
the surface of a block consists of 6 (3 pairs of) areas :
front and back
left and right
top and bottom
you know that the area of a rectangle is length × width ?
so,
front and back are
2× 9×13.5 = 18×13.5 = 243 m²
let and right are also
2× 9×13.5 = 243 m²
top and bottom are
2× 9×9 = 2 × 81 = 162 m²
so, for the whole package you need
243 + 243 + 162 = 648 m²
the money for that amount of wrapping paper alone would be way more than I ever spent on a teacher in my life ...