**This is a one-time need.**All of the installable / online solvers that I've used in the past can only handle up to 6 equations.

Equations:

p=R_1*M_1-R_1

p=R_2*M_2-R_2

p=R_3*M_3-R_3

p=R_4*M_4-R_4

p=R_5*M_5-R_5

p=R_6*M_6-R_6

p=R_7*M_7-R_7

p=R_8*M_8-R_8

R_1+R_2+R_3+R_4+R_5+R_6+R_7+R_8=S

Looking to Solve For:

p

R_1

R_2

R_3

R_4

R_5

R_6

R_7

R_8