[Solved!]Help with plotting Km on graph...

I'm a complete noob at excel so any help would be appreciated. Attached is a graph for an enzyme kinetics lab I had to do. I need to solve for KM(with the M subscripted) which is equal to 1/2Vmax. I know KM= 0.00065 and I know that at 0.00065 the substrate concentration is 0.5%, but I have no idea how to make a straight line go from that point to the y-axis and x-axis. It essentially has to look like this.

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I've tried for over an hour trying to plot points and try to figure it out, but to no avail. If anyone has any idea on how to do this, I'd appreciate it very much. Thanks in advance.

Hi,

Does the attached help