Aright triangle has legs measuring 4.5 meters and 1.5 meters.
the lenghts of the legs of a second triangle are proportional to the lengths of the legs of the first triangle.
what could be the lengths of the legs of the second triangle?

Well,

If the length of the legs of the second triangle are proportional to the lengths of the legs of the first triangle, we could simply multiply both of the dimensions by whole numbers and get an infinite number of proportional lengths.

Example:
4.5 * 2 = 9
1.5 * 2 = 3

A triangle with legs measuring 9 meters and 3 meters will be proportional to the first triangle with leg lengths of 4.5 and 1.5 meters, respectively.

More proportional lengths:
4.5 * 3 = 13.5
1.5 * 3 = 4.5

4.5 * 4 = 18
1.5 * 4 = 6