which process do i use first in solving this x(4x+1)^2?

Not sure, but.....

X(4X + 1)^2

Square first.

(4x + 1)(4X + 1)

16X^2 + 8X + 1

Distribute

X(16X^2 + 8X + 1)

16X^3 + 8X^2 + X

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PS: This is an expression, not an equation, so there is nothing to solve in that sense.