A microinstruction can't be further broken down into two or more. It can take more than a cycle if it involves a memory access. The first instruction given here isn't a microinstruction. It is an assembly lang instruction.
It can be broken down as:
T1 , T2: MAR<--SP
T3. : MDR<-- r , SP<-- SP-1 ( it is not mandatory to decrement it in this cycle. Anyway, it can be decremented locally)
T4, T5 : M [MAR] <-- MDR
The problem says, 8-bit MDR, 8-bit data bus, 8 bit registers.Can't you see that the given CPU is 8-bit? 8 multiplexers transfer 8 bits when selection input is 0 and 1 respectively. We certainly need to move 16-bit SP to 16-bit MAR via a 8-bit bus. So, 2 cycles to get SP to MAR. In total, we need 5 of them clock cycles to execute a push.
Thank me later.