Four objects are situated along the $y$ axis as follows: a $2.00-\mathrm{kg}$ object is at $+3.00 \mathrm{m},$ a $3.00-\mathrm{kg}$ object is at $+2.50 \mathrm{m},$ a 2.50 -kg object is at the origin, and a $4.00-\mathrm{kg}$ object is at $-0.500 \mathrm{m} .$ Where is the center of mass of these objects?