Hello.
First, let's calculate

Remember the Properties of Exponents:
If we have a number to a negative power, we flop the number over:

Now, let's use this property to simplify our expression.
Flop the number over:

Now, we should recall another property of exponents:

Since we have a fraction to a power, we should raise both the numerator and the denominator to the power:

3 cubed is 9, and 7 cubed is 343:

Now, the multiplicative inverse of that number is simply that number flopped over:

I hope it helps.
Have a great day.
