Question

Using cross multiplication how to you find n

Answer 1

Cross-multiply:  10(n-6) = 10n - 60 and 9n - 36.  Set these 2 results equal to each other:  10n - 60 = 9n - 36.  Then n=24.  By all means, check to ensure that this value n=24 actually satisfies the original equation.

Answer 2

Multiply both sides by the 2 denominators...if you do this you end up with:
10(n-6)=9(n-4)
10n-60 = 9n-36
10n-9n = -36 + 60
n=24