Answer: $29,950
Explanation: As we know that,
Economic profit = Total revenues - (explicit cost + implicit cost)
where,
Explicit costs are payments made to others for running operations of business.
Implicit cost or opportunity cost can be defined as the cost of loosing profits for choosing one alternative instead of other.
In the given case the interest of $50 on savings and $6000 salary is the implicit cost.
Economic profit = $90,000 - ($54,000 + $50 + $6,000)
= $29,950