Question 1025092
The 2 groups of pens are:
{{{ x }}} pens
{{{ 120 - x }}} pens
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{{{ 3x }}} is the cost of {{{ x }}} pens
{{{ 4*( 120 - x ) }}} is the cost of the remaining pens
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{{{ 3x + 4*( 120 - x ) }}} is the total cost of all 120 pens