Question 389679
{{{C(g) = 3.12*g
(a) {{{3.12}}} is the cost/gallon of gas
(b) {{{C(2) = 3.12*2}}}
{{{C(2) = 6.24}}}
(c) {{{C(9) = 3.12*9}}}
{{{C(9) = 28.08}}}
(d) The domain would be appropriate values 
for {{{g}}}, gallons of gas.
You could put {{{0}}} gallons in, but you
can't put (-) gallons in.
You can't put in more than the tank holds
So the domain is {{{T >= g >=0}}}
where {{{T}}} is capacity of tank in gallons
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The range is all appropriate values of {{{C(g)}}},
The cost of putting {{{g}}} gallons in
{{{C(g) >= 0}}} since Cost is either {{{0}}} or (+)
and {{{C(g) <= 3.12T}}}
range is {{{3.12T >= C(g) >= 0}}}