The formula to find the arc length of a circle = θ/360 ×2××r
The formula to find the area of a sector= θ/360××r²
The only thing missing is "θ"
The arc length is given to be 15cm so basically θ/360×2×3.14×12 = 15
θ= 360×15 ÷ 2×3.14×12 = 5400÷ 75.36= 71.65
now that we found "θ" we just continue with the formula to find the area of a sector (θ/360×r²)
=71.65×3.14×12²= 90cm
(it's a bit complicated but i hope this helped i tried to simplify it as much as i could)