S'(t)= -147.78e^(-0.2t)

Question

S=7389 units when t=0

find the function that describes the number of daily sales t days after the end of the campaign

Really stuck can someone help me to just find the function so I can head in the right track for the rest of the question


let f(t)= e^kt + C
then f'(t)= k e^kt

so here you are given S', integrate to get S. Don't forget the constant of integration.