X=60° (equilateral triangle)
y=120°
Working: (360°-120°)/2
I just took the test the answer is 9 cm.
Since 90 degree is 1/4 of a circle, the area will be 1/4 th area of the full circle.
The radius is given by, r = 8 ft, therefore, the area of the full circle is,

Therefore, the area of the sector is,

Loga x=n ⇔ a^n=x
log₇ 21=x
x=log ₇ 21
x=ln 21 / ln7=1.564575034...
Answer: x=log₇ 21