As it is store and forward mechanism so data will be forwarded from the switch when entire data is received on it..
Hence transmission time will be involved at 4 places : Source and 3 switches..
And there are 4 links hence 4 times the one link propogation delay involves..
Hence
Total delay = 4 * Transmission delay + 4 * Propogation delay
= 4 * ( Data size / Bandwidth + link length / speed of medium )
= 4 * ( (1500 * 8 / 100 * 106 ) * 106 + 12 )
= 4 * ( 120 + 12 )
= 4 * ( 132 )
= 528 μs
Hence total delay involved = 528 μs