BUBS is involved in the production of water suction engines. Production of this engine takes a standard time of 15 minutes. BUBS has budgeted the salary of workers working on this project at 10 per hour. BUBS has also budgeted that completing the engine requires an operation that lasts 350 times. It was subsequently realised that the standard time for producing the engine included in the budget did not incorporate expected time savings from the use of new machinery from the start of the period. The standard time should have been reduced to 12 minutes. The engine was actually carried out 370 times in the period in a total of 80 hours. The operatives were paid 850. Calculate the operational labour efficiency variance