To solve the equation given, we can use the properties of exponents. The equation can be expressed as follows:
\[ \frac{H^{450}}{H^a} = H^{215} \]
Using the property of exponents that states \(\frac{H^m}{H^n} = H^{m-n}\), we can simplify the left side:
\[ H^{450 - a} = H^{215} \]
Since the bases are the same (both are \(H\)), we can set the exponents equal to each other:
\[ 450 - a = 215 \]
Now, we can solve for \(a\). To do this, we can rearrange the equation:
\[ 450 - 215 = a \]
Calculating the left side gives:
\[ 235 = a \]
So, the missing exponent \(a\) is \(235\).