These aren't too bad, how far in math have you gone?

Really all you need to do is to define the the variables. For the first one, we'll let the time for John to complete a job be and we'll call the time for harry to complete the same job .

Now just write down what your told in terms of an equation. John can complete the job in 1/2 the time it takes harry. Therefore:

(the time it takes john is equal to 1/2 the time it takes harry.)

If they both work together, they can complete the job in four hours:

(the time it takes harry + the time it takes john, is equal to 4)

Now just solve the system of equations for the time it takes john: