answer : 12.4cm
explanation :
first find the circumference of the circle, the formula for that is 2 x pi x radius.
This means the circumference of your circle is equal to 2 x pi x 7.9. This equals 49.612.
As you’re working out the curve AB, you need to divide the circumference by 4 as AB is a quarter of the circle. 49.612 divided by 4 = 12.403
You need to round it up to the nearest tenth. The digit 0 stays the same when rounding so your answer = 12.4cm
Hope that helped :)