Lee takes 7 hours to mow all of the yards on his block. if his brother jj him, they are able to do the same job in 3 hours. how long would it take jj to do the job himself?

It will take JJ 4 hours to mow all of the yards in his block alone

Diameter of the semicircle = 10 km.

Explanation:  perimeter of semicircle =   1  2

the circumference + diameter  Given: perimeter of semicircle =  25.7  k m

Circumference of circle with radius  r =  2 π r  where  2 r = diameter  ⇒ 25.7 = 22 π r + 2 r ⇒ 25.7 = π r + 2 r = r ( π + 2 )  ⇒ 25.7 = r ( 3.14 + 2 ) = r ( 5.14 )  ⇒ r = =5m ⇒d i a m e t e r = 2 r = 10 k m