The answer to you question is 900
The factors of 28 are 1 x 28, 2 x 14, and 4 x 7. None of which add up to 20.
Not all triangles are similar, like all triangles, all angles must addd up to 180 degrees. Hope this helps.
if the order mattered it would be 7*6*5 *4*3 = 2520 arrangements
if order didn't matter
7*6*5*4*3*2 divided by (5*4*3*2*2) = 21
To find the simplest form of the ration divide the numerator and denominator by the GCF of both numbers. In this case the GCF is 10. (GCF means the Greatest Common Factor).
10÷10/50÷10 = 1/5
Best of Luck!