y=12*sqrt(18) -6*sqrt(20) -3*sqrt(50) +8*sqrt(45)
=12*sqrt(2*9) -6*sqrt(4*5) -3*sqrt(2*25) +8*sqrt(9*5)
=12*3*sqrt(2) -2*6*sqrt(5) -3*5*sqrt(2) +3*8*sqrt(5)
=36*sqrt(2) -15*sqrt(2) -12*sqrt(5) +24*sqrt(5)
=21*sqrt(2) +12*sqrt(5)
=21*1.414213562 +12*2.236067977
=29.69848481 +26.83281573
=56.53130054