8.15=(9.0*10^9)(-5.2*10^-5)(-5.2*10-5)/x

Multiply both sides by x:  8.15x  =  (9.0·10⁹)(-5.2·10^-5)(-5.2·10^-5)

Simplifying exponents:    8.15x  =  (9.0)·(-5.2)·(-5.2)·(10^-1)

Dividing:                              x  =  (9.0)·(-5.2)·(-5.2)·(10^-1) ÷ 8.15

Now, it's calculator time!