.
They want you solve equation
= 3.
From this equation,
7x = = 4*4*4 = 64,
x = .
ANSWER. x = .
Solved.
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To solve this problem, there is NO any need to change the base, as @MathLover1 does.
Is is an excessive operation, which actually is not needed.
Solving problems with excessive operations is NOT a good decoration. In opposite, it is a bad style.