Interview cost

Day

Evening

Children

$$20$

$$25$

No children

$$18$

$$20$

$[$Note: X$1=$ no$.$ of daytime interviews of households with children. $x2=$ no$.$ of evening interviews of households with children. $x3=$ no$.$ of daytime interviews of households without children. $x4=$ no$.$ of evening interviews of households without children.$]$

Which of the following constraints is correct?

$x_1+x_2+x_3+x_4<mn\; id="EditorElement\_2729619">2</mn><mn\; id="EditorElement\_2729620">0</mn><mn\; id="EditorElement\_2729621">0</mn><mn\; id="EditorElement\_2729622">0</mn>$

$x_1+x_2+x_3+x_4=2000$