Let the total number of cakes sold on Thursday and Saturday be \( T_T \) and \( T_S \) respectively, and let the number of Chocolate cakes sold on Thursday and Saturday be \( C_T \) and \( C_S \), respectively.
Step 1: Use the given ratio.
The ratio of Vanilla cakes sold on Thursday to Saturday is given as 3:4. Let the number of Vanilla cakes sold on Thursday and Saturday be \( V_T \) and \( V_S \), respectively. Therefore, we have:
\[
\frac{V_T}{V_S} = \frac{3}{4}
\]
This means:
\[
V_T = \frac{3}{4} \times V_S
\]
Step 2: Use the given Chocolate cakes condition.
We are also given that the number of Chocolate cakes sold on Thursday is equal to the number of Chocolate cakes sold on Saturday, so:
\[
C_T = C_S
\]
Step 3: Set up the total cake equation.
The total number of cakes sold on Thursday and Saturday can be written as:
\[
T_T = V_T + C_T, \quad T_S = V_S + C_S
\]
Since \( C_T = C_S \), we have:
\[
T_T = V_T + C_T, \quad T_S = V_S + C_T
\]
Substitute \( V_T = \frac{3}{4} \times V_S \) into the equation for \( T_T \):
\[
T_T = \frac{3}{4} \times V_S + C_T
\]
Now, substitute into the equation for \( T_S \):
\[
T_S = V_S + C_T
\]
Step 4: Find the relationship between \( T_T \) and \( T_S \).
We know that the number of Chocolate cakes sold on Saturday is equal to the total cakes sold on Monday, so we have:
\[
C_T = T_M
\]
Thus, the number of Chocolate cakes sold on Saturday is equal to the total number of cakes sold on Monday. Therefore, the correct answer is Monday.