Sum the ratio:
s = 5 + 3 = 8
to get the first amount:
a1 = (3/8) * 56 = 21 $
a2 = (5/8) * 56 = 35 $
Check:
total = 21 + 35 = 56 $ ( as given)
ratio = 35/21 = 5/3 (as required)
We know that out of 3000 people, 9 had a alergic reaction.
in this case our 100% is 3000, and we want to know what percentage is equivalent to those 9 that had a mild allergic reaction.
here we can use the rule of 3, this is:
if 3000 is equivalent to 100%, then 9 is equivalent to:
(9/3000)*100% = 0.3%
The answer is 19.6 cm^2
you should find the height of the triangle by heron formula: it will be 9.8
so the area is

good luck