9^2x-y+27^x-y=9^2x÷9^y+27^x÷27^y
=（3^x）⁴÷（3^y）²+（3^x）³÷（3^y）³
=4⁴÷6²+4³÷6³
=

64

9

+

8

27

=

192

27

+

8

27

=

200

27

．