To determine the measure of interior angle a in the quadrilateral formed by vertices a, b, c, and d, you need to consider the properties of the angles in a quadrilateral.
The sum of the interior angles in any quadrilateral is always 360 degrees. If you have the measures of the other three angles (b, c, and d), you can find angle a by the formula:
\[ \text{angle a} = 360^\circ - (\text{angle b} + \text{angle c} + \text{angle d}) \]
If you provide the values for angles b, c, and d, I can help you calculate the measure of angle a.