1. The problem asks for the measure of each interior angle in a regular polygon with 4 sides. 2. The formula to find the measure of each interior angle in a regular polygon is: $$\text{Each interior angle} = \frac{(n-2) \times 180}{n}$$ where $n$ is the number of sides. 3. For a polygon with 4 sides, substitute $n=4$ into the formula: $$\text{Each interior angle} = \frac{(4-2) \times 180}{4}$$ 4. Simplify the numerator: $$\frac{2 \times 180}{4}$$ 5. Calculate the multiplication: $$\frac{360}{4}$$ 6. Divide to find the angle measure: $$\cancel{\frac{360}{4}} = 90$$ 7. Therefore, each interior angle in a regular polygon with 4 sides is $90$ degrees.