Assuming a perfect pipeline with no stalls or hazards, the time it takes to complete 120 instructions with pipelining can be calculated as follows:
Time per stage = 5.3 nanoseconds
Number of stages = 5 (fetch, decode, execute, memory, writeback)
Number of instructions = 120
The number of cycles required to complete 120 instructions is equal to the number of stages, since each stage can be working on a different instruction at the same time. Therefore, the total time required is:
Total time = Time per stage x Number of stages x Number of cycles
Total time = 5.3 nanoseconds x 5 stages x 120 cycles
Total time = 3180 nanoseconds
Rounding to the nearest integer, the answer is 3180 nanoseconds.