Question 1014815
m+r+k=40

m = r/3

k=r+5

The three equations imply, by direct substitution, 

r/3 + r + (r+5) = 40

7r/3 = 35 after adding like terms and transposing the constant...

7r = 105 after cross-multiplication

r = 15

Meaning, Matt is 15/3 = 5 five years old, and Kathy is 15+5 = 20 years old.