Calculate the margin of error for a derived product

moe_product(est1, est2, moe1, moe2)

## Arguments

est1

The first factor in the multiplication equation (an estimate)

est2

The second factor in the multiplication equation (an estimate)

moe1

The margin of error of the first factor

moe2

The margin of error of the second factor

## Value

A margin of error for a derived product