20. Which of the following is equivalent to
the expression (i + 5)(3 + 4i)?
F 11 + 23i
G 15 + 19i
H 19 + 23i
J 23i

11+23i

simplified using Foil

To do this, I'd create an equation. 
here's what we're given: 
- the total angle is 90 degrees 
-one part of the angle is 2x 
- the other part is 3x + 15 

So you could pretty much make this an addition sequence: 

2x + 3x + 15= 90 

combine like terms 

5x + 15= 90 
5x=90-15
5x= 75 
x= 15 

now you know x, so substitute x=15 into the two expressions for the measurements of the angles 

1) 2(15)= 30 
2) 3(15) + 15= 60 

and you know this is correct because if you add the two answers together, you get 90 !!! 

hope this makes sense :)