Working out the expression 7(3ˣ) is first to calculate the value of 3ˣ then multiply the answer to 7.
For example, let x = 2
Then 7(3ˣ) = 7(3²) = 7 × 9 = 63
With the same value of x = 2, calculating 21ˣ = 21² = 441, which isn't the same answer with the expression 7(3ˣ)
Answer: a = -3
Explanations:
The given equation is:

This can be re-written as:

Collect like terms:

Cross multiply:

To verify if the solution is correct, substitute a = -3 into the question given. If the Right Hand Side equals the Left Hand Side, then the solution is correct.

Since the Left Hand Side = Right Hand Side = 7, the solution a = -3 is correct
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