Question 984294
Let the number of days worked be W. The the number of day absent is
{{{A = 20 - W}}}

The pay is defined by the equation
{{{Pay = 120*W - 10*A}}}
{{{1880 = 120W - 10(20-W)}}}
{{{1880 = 120W - 200 + 10W}}}
{{{1880 + 200 = 120W + 10W}}}
{{{2080 = 130W}}}
{{{2080/110 = W}}}
{{{16 = W}}}

So if they worked 16 days, they must have been absent 4