Given the mapping of registers to variables below, write a program to implement the following expression:

$Z=(A+B)(C-D)$

Ex: If the values of $x8,x9,x18,$ and $x19$ are initialized in the simulator as:

then $18$ is stored in $20.$

Note: Use the $\text{'}+\text{'}$ button under the Registers display to initialize register values.