What is the measure of minor arc ab? (picture attached)

The measurement is 45.

Step-by-step explanation:

1/8 of 360 is 45 and 45 is half of 90.

One angle is 40 degrees and the other is 50 degrees.

A complementary angle is 90 degrees.

As the ratio is 4:5 we can use the equation: 4x+5x=90

Solving it we get:
9x=90
x=10.

So the ratio is 4(10):5(10)

Meaning the two angles are 40 degrees and 50 degrees.

I hope this helps!
(And if you can, could I have brainliest please?)