draw dagarm (see attachment)
we've got a right triangle
the legs are 12 and 15
and the hypohuse is the diagonal
remember, for any right tirnalge
when the legs are a and b and hytponuse is c then
a²+b²=c²
so
12²+15²=c²
144+225=c²
369=c²
sqrt both sides
√369=c
3√41=c
the diagonal is 3√41 m or about 19.2m
