First, a bit of housekeeping:
The meaning of four consecutive even numbers is 15. Wouldn't that be "mean," not meaning? Very different concepts!
The greatest of these numbers is _______ a^1
"a^1" means "a to the first power. There are no powers in this problem statement. Perhaps you meant just "a" or "a_1" or a(1).
The least of these numbers is ______a^2.
No powers in this problem statement. Perhaps you meant a_2 or a(2)
In this problem you have four numbers. All are even, and there's a spacing of 2 units between each pair of numbers (consecutive even).
The mean, or arithmetic average, of these numbers is (a+b+c+d) / 4, where a, b, c and d represent the four consecutive even numbers. Here this mean is 15. The mean is most likely positioned between b anc c.
So here's what we have: a+b+c+d
------------- = 15
4
This is equivalent to a+b+c+d = 60.
Since the numbers a, b, c and d are consecutive even integers, let's try this:
a + (a+2) + (a+4) + (a+6) = 60. Then 4a+2+4+6=60, or 4a = 48, or a=12.
Then a=12, b=14, c=16 and d=18. Note how (12+14+16+18) / 4 = 15, which is the given mean.
We could also type, "a(1)=12, a(2)=14, a(3) = 16, and a(4) = 18.