I would really like to get some help :)

Answer: I don't know about the formula, but consider the logic below.
Step-by-step explanation:
Martina = 12
Joey = 0
12 x 3 = 36
36 - 3 = 33
If Joey was 21, Martina would be 33.
Answer:
y = 15
Step-by-step explanation:
in 3 years Martina would be 15 and joey would be 5.
5 · 3 is 15 so
x being joey
y being martina
x · 3 = 15