Can someone please assist me with this?

(9/49)^(-3/2)

I do this thingy

1/(9/49)^(3/2)

Then I do this thingy

(49/9)^(3/2)

Then I do this thingy

(Square Root of (49/9))^3

I'm now lost...

ok, then you have

(7/3)^3 and you can do that.