To solve the problem in the image:

We are given:

• Principal $P = 840$ dollars
• Annual interest rate $r = 2\% = 0.02$
• Time $t = 6$ months, which is $\frac{6}{12} = 0.5$ years, since the interest rate is annual.

The formula for simple interest is:

$I = P \times r \times t$

Substituting the given values:

$I = 840 \times 0.02 \times 0.5 = 8.40 \, \text{dollars}$

Thus, Marc will earn $8.40 in interest after 6 months.

Would you like more details on this calculation or have any questions? Here are some related questions to explore:

1. What would Marc earn in interest after 1 year?
2. How does simple interest differ from compound interest?
3. What is the formula for compound interest, and how would the answer change with it?
4. How would the interest change if the rate was 3% instead of 2%?
5. If Marc made monthly deposits into this account, how would that affect the total interest earned?

Tip: When calculating interest, ensure you match the time units (months vs. years) with the interest rate given to avoid mistakes!