A small shop in Bulacan fabricates threshers for palay producers in the locality. The shop can produce each thresher at a labor cost of P$1800.$ The cost of materials for each unit is P$2500.$ The variable costs amounts to P$650/$unit$,$ while fixed charges incurred$/$annum totals P$69000.$ If the portable threshers are sold at P$7800/$unit$,$ how many units must be produced and sold per annum to break even?