2.5*[1/(6.1-6.09)]
=2.5*1/0.01
=2.5*100
=2500
4.21*99+42.1*0.1
=4.21*99+4.21*10*0.1
=4.21*99+4.21*1
=4.21*(99+1)
=4.21*100
=421