Suppose that in 250 memory references there are 30 misses in first level cache and 10 misses in second level cache. Assume that miss penalty from the L2 cache memory are 50 cycles. The hit time of L2 cache is 10 cycles. The hit time of the L1 cache is 5 cycles. If there are 1.25 memory references per instruction, then the average stall cycles per instruction is ________.