solve[{x+a=s+p, y+b=q+t, (x^2+y^2)^(1/2)+(a^2+b^2)^(1/2)=(s^2+t^2)^(1/2)+(p^2+q^2)^(1/2), x^2+y^2+a^2+b^2=(4/5)*(s^2+t^2+p^2+q^2) }, {s, t, p, q}]