-140

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

-100

-145.52786404500042060718165266254

3x=90 x= 30 ...(1)

30 -2x=20, 2x=-10, x=5 ....(2)

5+ x²=25, x²=20, x=√20=4.472 ....(3)

√20 - (30 x 5) = 4.472-150 = - 145.528

Since the definition is not given in the last line, then the following must be assumed following mathematical principles. (Multiplication before addition/subtraction)

- 140