I am not sure of the answer which one of the option is it?

Step-by-step explanation:

well, there are a few things you have to burn into your brain for all times. one of these is : the sum of all angles in a triangle is always 180 degrees. it does not matter what type of triangle it is. the sum is always 180 degrees.

so,

180 = A + 80 + 40

60 degrees = A

so, B. is the right answer.

5   1/4   miles per hour

step-by-step explanation:

15   3/4 / 3 = 5   1/4

60°

step-by-step explanation:

the measure angle of c in an isosceles triangle abc is 60° because in isosceles triangle,the measures of all the angles is 60°.