We know that When circles have the same central angle measure, the ratio of measure of the sectors is the same as the ratio of the radii squared. so rA²/rB²=A/B where rA-------> radius circle A rB------> radius circle B A------> area sector A B------> area sector B rB²=B*rA²/A-------> 6²*[40π]/[10π]-------> 144--------> rB=√144 rB=12 m