Calculate 2/3 of 30: Teacher's Essay Marking Problem

To determine how many essays Steve has marked when he finishes $\frac{2}{3}$ of the total, we perform the following calculation:

• Step 1: Identify the total number of essays, which is 30.
• Step 2: Determine the fraction of essays that are marked, $\frac{2}{3}$.
• Step 3: Multiply the total essays by the fraction marked:

$\frac{2}{3} \times 30 = \frac{2 \times 30}{3} = \frac{60}{3} = 20$

Therefore, Steve has marked 20 essays.

Thus, the correct number of essays Steve has marked is $\boxed{20}$.