Question 889092
Let Bobby's age be "b"
    Arianna's age be "a"

b = 3 + 2a    (The first equation)

b + a = 9     (The second equation)
3 + 2a + a = 9(Substitution)
3 + 3a = 9
3a = 6
a = 2

b = 3 + 2(2)
b = 7

Therefore, Bobby's age is 7 years old and Arianna is 2 years old.