$16.80 / 4 gallons = $4.20 per gallon
12 black and white, 18 color in one row
6 black and white, 9 color in two rows
4 black and white, 6 color in three rows
2 black and white, 3 color in six rows
Answer:
d ≤ -0.5
Step-by-step explanation:
Multiply each term by -1
What number do you need help with
When
, we have


and of course 3 | 6. ("3 divides 6", in case the notation is unfamiliar.)
Suppose this is true for
, that

Now for
, we have

so we know the left side is at least divisible by
by our assumption.
It remains to show that

which is easily done with Fermat's little theorem. It says

where
is prime and
is any integer. Then for any positive integer
,

Furthermore,

which goes all the way down to

So, we find that

QED