Video streaming company A charges a one-time $40 membership fee and $2 per video stream. Video streaming company B charges a one-time $20 membership fee and $4 per video stream. Let the variable s represent the amount of videos streamed and let the variable c represent the cost. For how many video streams will the cost be the same for both companies? Which system of equations can be used to solve this problem?
A: {c=40s+2c=20s+4
B: {c=42sc=24s
C: {c=40−2sc=20−4s
D: {c=40+2sc=20+4s