Is it normal to forget things almost 4 months after a concussion?

Yes I've had that too

Step-by-step explanation:

I had mine for about 5-6 months

Yes, a concussion can cause long-term memory loss and recurring short-term memory loss, even weeks, months, or years after the head trauma. Usually, this is known as a symptom of post-concussion syndrome

just get this app called photo math it should be able to do those