Answer:
(C) 18
Step-by-step explanation:
We can create a systems of equations. Assuming 
is Michelle's age, 
is Joan's age, and 
is Ryan's age, the equations are:
We can use substitution, since we know the "values" of m and j.
So we know that Joan is 18 years old.
Hope this helped!
Answer:
27KG
Step-by-step explanation:
Mouse- M , Cat - C, Dog - D
M + C = 10 ----- (1)
M + D = 20 -------(2)
C + D = 24 --------(3)
(1) - (2) => C - D = -10 ---- (4)
(3) + (4) => 2C = 14
=> C = 7
Substitute C in (1) => M + 7 = 10
=> M = 3
Substitute M in (2) => 3 + D = 20
=> D = 17
Therefore C + M + D = 7 + 3 + 17 = 27KG
