How to find joint distribution probability from joint density?

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Area $D$ is defined as the enclosed area by the points $(0,0),(2,0),(0,2),(2,8)$. Point $(X,Y)$ is chosen randomly from $D$ with uniform density. Need to calculate the joint distribution function $F_{X,Y}$ at $(1,7)$

I calculated that the density in $D$ is 0.1, and I noticed that the point is outside the area, but the answer is clearly not zero. So what to do?