solver for 4 equation

i have the following equations and i want to know how to use solver to find what a,b,c and d. can someone help, thank you.

a+b = 10
a+c = 20
a+d = 30
b+c+d = 0

I don't know that Solver is the best tool for this (the built in matrix functions might be better), but it will work just fine.

Basically, you need to set up the spreadsheet. Pick four cells to contain a, b, c, and d. Then in four other cells put formulas to calculate the four sums. Then call Solver, tell it to set one of the sums to it's desired value subject to the constraints that the other three sums are equal to their desired values.