Question 172025
(1)
If {{{x}}} is the number of years since 1980, then in 1980 {{{x = 0}}}
Putting this into the equation for N. America,
{{{-5.4*0 + y = 372}}}
{{{y = 372}}}
There were 372 million people in N. America in 1980
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In 2000, {{{x = 20}}}
{{{-5.4*20 + y = 372}}}
{{{-108 + y = 372}}}
{{{y = 372 + 108}}}
{{{y = 480}}}
There were 480 million people in N. America in 2000
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In 2010, there will be
{{{-5.4*30 + y = 372}}}
{{{y = 372 + 162}}}
{{{y = 534}}}
There will be 534 million people in N. America in 2010
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(2)
In S. America, in 1980
{{{-5.25*0 + y = 242}}}
{{{y = 242}}}
There were 242 million people in S. America in 1980
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In 2000
{{{-5.25*20 + y = 242}}}
{{{-105 + y = 242}}}
{{{y = 347}}}
There were 347 million people in S. America in 2000
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In 2010,
{{{-5.25*30 + y = 242}}}
{{{-157.5 + y = 242}}}
{{{y = 399.5}}} 
There will be 399.5 million people in S. America in 2010