Do I require loading in this example of load store architecture?
You need to load x into R before you store R into b

wikipedia says:

In computer engineering a load/store architecture only allows memory to be accessed by load and store operations, and all values for an operation need to be loaded from memory and be present in registers. Following the operation, the result needs to be stored back to memory.

In your case, x is still in memory and has to be loaded into a register.