Answer:
492.99
Step-by-step explanation: x = amount invested at 12%
y = amount invested at 9%
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x + y = 20287
0.12x = 0.09y + 492.99
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put the system of linear equations into standard form
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x + y = 20287
0.12x - 0.09y = 492.99
E

e=mfg
Where m is a constant of proportionality;
e=4, f=2 and g=8
Then;
4=m*2*8
4=16m
m=0.25
Cost per mile = 

= 0.97
Now,
c - cost for gasoline and maintenance and
m - number of miles traveled
Hence, the required expression is c = 0.97m.
Density= mass ÷ volume
Density= 5.28 ÷ 2
Density= 2.64 cm3