Plz help me solve this small equation plz show working

Thank you so much

How do you use the additive inverse to evaluate an expression that uses subtraction in a full sentence

Hart manufacturing had six-month sales of $80 million, with $20 million of that amount from the internet. it set a goal to increase the percentage of total sales coming from the internet by 4 percent in the next six months. the results were total sales of $85 million. if the company meets its goal exactly, what will the dollar amount of internet sales be?

Situation: an archaelogist in turkey discovers a spear head that contains 54% of its original amount of c-14. n = noekt no = inital amount of c-14 (at time t = 0) n = amount of c-14 at time t k = 0.0001 t = time, in years find the age of the spear head to the nearest year