What would be the answer to this equation with error?

What a strange equation. Most values with uncertainties will also have units, since they represent measured values, and measured values are usually measured in some kind of units.

Be that as it may, the "answer" is

1.39π(9.16)²

I'd get the uncertainty in the answer with the error propagation formula. It's easier with symbols. Let the answer be "a", 1.39 = b, and 9.16 = c. Then a = bπc².

Δa = √{(da/db ∙ Δb)² + (da/dc ∙ Δc)² }

where the partial derivatives da/db = πc² and da/dc = 2bπc, so

Δa = √{(πc² ∙ Δb)² + (2bπc ∙ Δc)² }

Δa = √{[π(9.16)² ∙ (0.005)]² + [2(1.39)π(9.16) ∙ (0.005)]² }