Answer:
Total number of milkshakes sold on Monday = 300
Number of milkshakes without whipped cream = 90
Step-by-step explanation:
Given:
Adrienne adds whipped cream to 210 milk shakes which is 70% of the total milk shakes sold.
To find the total milkshakes sold.
Solution:
Let the total number of milkshakes sold on Monday be = 
Percentage of milkshakes with whipped cream added to them = 70%
Number of milk shakes with added whipped cream can be given as:
⇒ 
⇒ 
⇒
[Representing percent in fraction form]
⇒
[evaluating in decimals]
We know that the number of milkshakes with whipped cream added to them = 210.
So, we have:

Solving for 
Dividing both sides by 0.7

∴ 
Thus, total number of milkshakes sold on Monday = 300
Number of milkshakes without whipped cream =
= 90