Answer:
- 18) 30°, 
 - 19) 38, 
 - 20) 41.34.
 
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Since P is incenter, we have properties of incenter applicable to given questions:
- P is the intersection of angle bisectors;
 - P is equidistant from the sides of the triangle.
 
Question 18
Since JN is angle bisector of ∠J, set up equation:
- 7x - 6 = 5x + 4
 - 7x - 5x = 4 + 6
 - 2x = 10
 - x = 6
 
Angle measures of the triangle are:
- m∠J = 2 (5*6 + 4) = 3(34) = 68
 - m∠L = 2(26) = 52
 
Then, according to triangle sum:
- m∠K = 180 - (68 + 52) = 180 - 120 = 60
 
Then, find the missing angle:
Question 19
Sides are equidistant from incenter:
Set up equation and solve or x:
- 9x - 34 = 3x + 14
 - 9x - 3x = 14 + 34
 - 6x = 48
 - x = 8
 
Find one of equal segments:
- PN = 3*8 + 14 = 24 + 14 = 38
 
Hence, MP = 38
Question 20
ΔMPJ and ΔOPJ are congruent right triangles as MP = OP and JP is common hypotenuse, therefore JM and JO are congruent as corresponding sides:
- 2x + 3 = 5x - 45
 - 5x - 2x = 3 + 45
 - 3x = 48
 - x = 16
 
Then JM is:
- JM = 2*16 + 3 = 32 + 3 = 35
 
We know MP = NP = 22. 
Find JP using Pythagorean:
- JP = 
