Explanation:
that actually depends on what sides correlate between both triangles and therefore on the length of the 3rd side of the second triangle.
but ok. here we find the answer, also because we know that there must be one common constant of proportionality (scale factor).
the questing is, does 48 correlate to 8 or to 15 ? and 90 to 15 or 17 ?
we see that 48/8 = 6, and that 90/15 = 6.
there we have it. no other combination gives us an identical factor.
so the constant of proportionality from small to large is 6.