b) `(-11^{5}.13^{7})/(11^{5}.13^{8})``=(-1.13^{7})/(1.13^{8})``= (-1.1)/(1.13)``= -1/13`
c) `(2^{10}.3^{10}-2^{10}.3^{9})/(2^{9}.3^{10})``= (2^{10}.3^{9}.(3-1))/(2^{9}.3^{10})``= (2^{10}.3^{9}.2)/(2^{9}.3^{10})`
`= (2.3^{9}.2)/(1.3^{10})``= (2.1.2)/(1.3)=(2.2)/3``= 4/3`