Apr 26, 2017, 00:2104/26/17
technically, 4 eqns & 6 unknowns has no explicit solution. (note the double ax & single ax are different symbols. as is the quiver with 5 arrows & 4 arrows.)
given that the double ax is a special representation, i'll assume a simple "2x".
so x+x+x=90 => x=30,
x-y-y=20 => y=5 then an assumption the 4 quiver is =4,
5+2z=25 => z=10,
so z-x * 4= ? => assuming standard operation precedence, = -110