The dashed line shows how you cut the bottom of a rectangular door so it opens more easily.  what is the new angle at the bottom left side of the door?

See the picture attached to better understand the problem

we know that
m ∠ACD=91.5°
m ∠ACD+m ∠ACB=180°-------> by supplementary angles
so
m ∠ACB=180-91.5-----> m ∠ACB=88.5°

m∠CAB+m ∠ACB=90°-----> by complementary angles
so
m ∠CAB=90-88.5-----> 1.5°
m∠ CAB is the new angle at the bottom left side of the door

the answer is
1.5°

It can be anything greater than -15f