Answer:
Principle for account B is greater.
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Step-by-step explanation:
First of all, let us have a look at the formula for Simple Interest:

Where
is the principle amount
is the Rate of interest per annum
is the time in years.
Time = 21 months = 

Let the Principles be
.
Using the formula for Simple Interest, we get:


Therefore, <em>principle for account B is greater</em>.
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