Calculate Angle D in ABCD Deltoid: Given Angles 30° and 40°

We know that in a kite, the side angles are equal to each other, meaning:

$B=C=70$

And therefore also:

$ACB=30$

$BCD=40$

Now we can calculate angle A. As we know, the sum of angles in a triangle is 180, so:

$180-30-30=120$

Now we can calculate angle D. As we know, the sum of angles in a kite is 360, so:

$360-120-70-70=100$

$D=100$