Question 721832
The given points are:
( x1,y1 ) = ( 1.75, 57 )
( x2,y2 ) = ( 2.75, 13 )
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Use the point-slope formula
{{{ ( y - 13 ) / ( x - 2.75 ) = ( 57 - 13 ) / (  1.75 - 2.75 ) }}}
{{{ ( y - 13 ) / ( x - 2.75 ) = 44 / (-1) }}}
{{{ y - 13 = -44*( x - 2.75 ) }}}
{{{ y = -44x + 121 + 13 }}}
{{{ y = -44x + 134 }}} answer
If the cost is $1.50,
{{{ y = -44*1.5 + 134 }}}
{{{ y = -66 + 134 }}} 
{{{ y = 68 }}}
68 apples/day will sell if the price is $1.50/apple
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check:
Does the line go through  ( 1.75, 57 ) ?
{{{ y = -44x + 134 }}}
{{{ 57 = -44*1.75 + 134 }}} 
{{{ 57 = -77 + 134 }}}
{{{ 57 = 57 }}}
OK
You can check the other point