How do you solve these two similar questions,
1) point masses 2g, 4g, 5g ang 1g are situated at points A, B, C and D with the position vector 3i -4j, -i + 5j, i +7j, and 5i + j respectively. find the position vector of the centre of mass for these four particles.
2) point masses 1g, 2g, and 5g are situated at the points A, B and C, with position vector 2i + j, i + 2j, and i - 3j respectively. find the position vector of the centre of mass for these three particles. If the 1g and 2g masses have their positions swapped, what is the consequent change in the x position of the centre of mass.