Question

solve for p, c, s, & t: 2p+c+s=20; t+2c+s=18; c+t+2c=16; s+c+p+t=21

Answer 1

You can solve for p, c, s, t, one at a time, but that's all.

For example:  If t + 2c + s = 18, t = 18 - (2c + s)