What is the equivalent mathematical sentence for “four decreased b a number x divided by five more than thrice a number x”?

What is the equivalent mathematical sentence for “the difference of fifteen and twice a number y divided by the sum of twenty and thrice a number x ”?

What is the equivalent mathematical sentence “One-fourth of a number y multiplied by three fifth of the number x”?

Kirsten can clean the house in 3 times as fast as Sophia, it takes them 4 hours to finish the work? How long would it take if Sophia will clean the house alone?

Kirby can paint a wall in 6 hours, but Conrad needs 4 hours to paint the same wall. How does it take them to paint the wall if they work together?