Question 473955
The linear function looks like
{{{ y = m*x + b }}}
where {{{ m }}} = slope
and {{{ b }}} = y-intercept
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For this problem:
Replace {{{y}}} with {{{ E(t) }}}
Replace {{{ x }}} with {{{ t }}}
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Now you have
{{{ E(t) = m*t + b }}}
Note that when {{{ t = 0 }}}, {{{ E(0) = b }}}
and {{{ E(0) = 64.1 }}}
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Now you have
{{{ E(t) = m*t + 64.1 }}}
Now you have to find {{{m}}}, the slope of the line
{{{m}}} is the change in {{{ E{t) }}} divided by 
the change in {{{ t }}}
{{{ m = ( 66.5 - 64.1 ) / (4 - 0) }}}
{{{ m = 2.4 / 4 }}}
{{{ m = .6 }}}
Now you have
{{{ E(t) = .6t + 64.1 }}}
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check answer:
{{{ E(4) = .6*4 + 64.1 }}}
{{{ E(4)  = 2.4 + 64.1 }}}
{{{ E(4) = 66.5 }}}
OK