Basic Center of mass problem. Need assistance

[blackbyron]

Homework Statement

Two point-like masses have common center of mass located at (xc=2.1cm, yc=4.3cm). Mass M1=49kg is at (x1=65cm, y1). Mass M2=7.5kg is at (x2, y2=(-85)cm). A third mass M3 is placed at (x3=(-15.3)cm, y3=9.4cm). What is the mass of M3 if the x-coordinate of the center of mass of the 3 mass is at x=0?

Homework Equations

$$\sum (mi)(xi)/(mi)$$ with respect to x.

The Attempt at a Solution

Find out the mass of m3, but what does this mean "x-coordinate of the center of mass of the 3 mass is at x=0?"

I cannot solve for m3 because the x2 is unknown.

Any ideas?

Thanks

 

[gneill]

Find the missing value of x2 using the initial center of mass for the two first masses.

I think that they meant to write, "x-coordinate of the center of mass of the 3 masses is at x=0".

 

[blackbyron]

Thanks for your reply. Yeah I was confused on "3 mass." I thought he meant the 3rd mass. But I just figured out because I admit that I didn't read it carefully though. However, thanks though, I appreciate it.