The formulas for the circumference and area of a circle are
[tex] C = 2\pi r,\quad A = \pi r^2 [/tex]
So, if we isolate the radius from the formula for the circumference we have
[tex] r = \dfrac{C}{2\pi} [/tex]
And if we substitute this expression for the radius in the formula for the area, we have
[tex] A = \pi r^2 = \pi \dfrac{C^2}{4\pi^2} = \dfrac{C^2}{4\pi} [/tex]
So, if you plug your value you have
[tex] A = \dfrac{144}{4\pi} = 11.4591559\ldots \approx 11 [/tex]
