To simplify the expression \( \frac{t^{400}}{t^{100}} \) using the Quotient Rule of Integer Exponents, you can apply the rule which states:
\[ \frac{a^m}{a^n} = a^{m-n} \]
In this case, we have:
\[ \frac{t^{400}}{t^{100}} = t^{400 - 100} = t^{300} \]
Thus, the simplified expression is \( t^{300} \).
The correct answer is:
a. \( t^{300} \)