<PRE><B>Question 1163295</B>
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Amount of gas (gallons)
18
12
8
Number of miles driven
90
360
540
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&lt;pre&gt;
x, miles driven   y, amount of gasoline in tank
  90                18
  360               12
  540                8
&lt;/pre&gt;
Checking slopes
{{{(12-18)/(360-90)=-6/270=-1/45}}}
and
{{{(8-12)/(540-360)=-4/180=-1/45}}}


Picking first point in the list
{{{y-18=(1/45)(x-90)}}}

{{{y-18=-x/45+2}}}

{{{y=-x/45+20}}}
or if you want name of function to be M, then  {{{highlight(M(x)=-(1/45)x+20)}}}.</PRE>