Answer:
The markup (in percentage) is 66.67%
The markup (in dollars) is $33.92
Explanation:
First, we will find the sales price of the product (excluding sales tax).
Let sales price be "x", so we can say:
x increased by 6.25% is 90.10
Note: 6.25/100 = 0.0625
Thus, we can write an equation and solve for x now:

The markup is a percentage of the cost.
The markup is the difference in cost and sales price, divided by cost. Then we multiply by 100 to get percentage. So:
MarkUp =

The markup (in percentage) is 66.67%
In dollars, it will be $33.92