There are four tasks on my to$-$do list: laundry $($L$),$ sweeping $($S$),$ groceries $($G$),$ and exercise

$($E$).$ How many choices for an ordered list of tasks are there if $...$

$($a$)$ I do one task this morning and then a second task this afternoon? First list the options, then

show how to count using Steps.

$($b$)$ I do one task this morning and then a second task this afternoon, but I refuse to do both

laundry and sweeping. Draw a tree to count. Explain why the Steps Rule does not apply.

Can you find a quicker way to count using part $($a$)$ and that the only disallowed options are

LS and SL$?$