Does “at least $100” mean the total must be less than, greater than, or greater than or equal to $100? Decide which inequality symbol ($<$, $>$, $\le$, $\ge$) matches that idea.

Once you know the expression for total earnings and which inequality symbol to use, compare that to each answer choice. Be careful not to mix up the 4 and 6 or the direction of the inequality sign.

Pick simple numbers for $s$ and $l$ that would give Oscar exactly $100 based on the problem description. For example, in Desmos, type 4*10 + 6*10 and note the output. This represents doing 10 small and 10 large deliveries.

For each answer choice, plug $s=10$ and $l=10$ into the expression in Desmos. For example, type 4*10 + 6*10 <= 100 for one option and see whether it evaluates to true or false. Repeat for the other choices using the appropriate expressions and inequality signs.

Choose numbers of packages that clearly earn more than $100 (for instance, increase either $s$ or $l$) and again use Desmos to check each inequality with those values. The correct inequality will evaluate to true both when the total is exactly $100 and when the total is greater than $100, while incorrect inequalities will fail one of these tests.

Oscar earns $4$ dollars for each small package and $6$ dollars for each large package.

• Money from small packages: $4s$
• Money from large packages: $6l$

So his total earnings for the day can be written as the sum of these two amounts:

The phrase “at least $100” means the total can be $100 or more, not less than $100.

In inequality form, “at least $100” is written with a greater than or equal to sign:

From Step 1, the total earnings are $4s + 6l$.

From Step 2, these total earnings must satisfy

Substitute $4s + 6l$ for “total earnings” to get the inequality that must be true:

So the correct choice is $4s + 6l \ge 100$.