Alan

A linear relationship means that you can write  C = m*d + k where m and k are constants to be found from the information you are given.

From May:  360 = m*500 + k  ...(1)

From June:  440 = m*900 + k ...(2)

Re-write (1) as k = 360 - m*500 and put this into (2)

440 = m*900 + 360 - m*500

Rearrange and simplify:

440 - 360 = m*400

80 = m*400

m = 80/400 = 0.2  ...(3)

Use (3) in (1)  (or (2) if you prefer)

360 = 0.2*500 + k

k = 360 - 0.2*500 = 360 - 100 = 260

So, in general

C = 0.2*d + 260

so when d = 1200 the cost is

C = 0.2*1200 + 260 = 500

Cost of driving 1200 miles is $500

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No, the first one is (x - 2)² + (y - (-8))² = 9², or (x - 2)² + (y + 8)² = 9²

2⁷ = 128 so x = 7

I assume the equation is 

where the overbar indicates the complex conjugate.

Then:

Nice one heureka!  Now do it for cubic, quartic, exponential,  ... etc. functions!

Life is complicated enough - let's keep it simple!!

You can have a point from me for lateral thinking anyway!

You are correct Melody; though it would probably be better to say "rearrange" your last equation, rather than "solve" it.  Doing this you get

$$y=-2x+\frac{5}{7}$$

or, if you prefer, by multiplying through by 7 and rearranging:

$$14x+7y=5$$