Answer
Let ABCD be a trapezium with parallel sides AB and CD
Let AB=20 ....... (Given) and CD=x
A(□ABCD)=480 m
2
,height(h)=15 m .......... (Given)
We know that, A(□ABCD)=
2
(AB+CD)
×h
⟹480=
2
20+x
×15
⟹
15
2×480
=20+x
⟹64=20+x
⟹x=44
Hence, length of other parallel side CD is 44 m.