Figuring out that I could move helped, but having to do that and then also move my mouse to click and focus on the text box made this feel extra difficult. The player already has one hand to keys for movement and one on the mouse to turn the gun and fire. I like the added difficulty of doing quick math and typing the answers to get more ammo, but having to completely stop to click on the text input box means I have to stop moving for too long and the game is over before it really begins.
Tldr; Allowing the game to capture these answers at any point would make the gameplay a lot less frustrating.
I was thinking after playing this that maybe it would feel better if bullets didn't stop at the first target and rather kept traveling through several. Then I saw in the comments that a shotgun is unlocked at some point, so that's probably a void consideration.
It's definitely not a bad game and I hope my initial comment was not discouraging. It just came across to me as similar to some other rage-inducing titles that are designed to get blood pumping with multiple things to manage and I don't typically fare well at those. 🙃