We are asked to find the measure of ∠CEB using the given information. Let's notice that, since diagonals in a rectangle are congruent and bisect each other, AE=DE. This means that triangle AED is an isosceles triangle and m∠DAE=m∠ ADE.
Using the Triangle Sum Theorem, we can find the measure of ∠DEA. Let's recall that according to this theorem the sum of the measures of angles in a triangle is always 180. We will use the fact we found above that m∠DAE=m∠ADE.
We found that the measure of ∠DEA is 50. Let's notice that angles ∠DEA and ∠CEB are congruent as they are vertical angles. Therefore, the measure of ∠CEB is also 50.
