incorrect answer in practice question? L1 Economic MPC

Is this incorrect because the feedback also calculates 4.2 billion as the answer... can someone pls help

https://preview.redd.it/a5fe4axb8f0g1.png?width=1522&format=png&auto=webp&s=1446057a07060d39ea62c99fc31b6bd3e672819b