Reciprocal of -7/9 is

Simplify :

1/10×1/10 = 

Mala and Latha each had a number of bangles. Mala said to Latha "If you give me 4  of your bangles, my number will be thrice yours". Laytha replied "If you give me 36, my number will be thrice yours". What is the total bangles together with them

A and B can complete a work individually in 12 days and 18 days. They started doing the work together but after 4 days A had to leave and B alone completed the remaining work. The whole work was completed in

If A and B can do a work in 6 days. B and C can do it in 12 days, C and A can do it in 4 days how many days it would take to finish the same work by all the three together