Answer:
a. Let's call the first number x which would make the other 2 numbers x + 2 and x + 4. Since they have a sum of 54 we can write:
x + x + 2 + x + 4 = 54
3x + 6 = 54
3x = 48
x = 16 so the numbers are 16, 18, 20.
d. We can write:
30 + x = 4(3 + x)
30 + x = 12 + 4x
18 = 3x
x = 6 years