Kirnon Clinic uses client$-$visits as its measure of activity. During July, the clinic budgeted for $3,600$ client$-$visits, but its actual level of activity was $3,520$ client$-$visits. The clinic has provided the following data concerning the formulas to be used in its budgeting:

Fixed element per month Variable element per client$-$visit

Revenue $ $0$ $ $39\mathrm{.}80$

Personnel expenses $ $35,800$ $ $11\mathrm{.}00$

Medical supplies $1,8007\mathrm{.}80$

Occupancy expenses $8,8001\mathrm{.}80$

Administrative expenses $5,8000\mathrm{.}90$

Total expenses $ $52,200$ $ $21\mathrm{.}50$

The activity variance for net operating income in July would be closest to: