What is 1 times 1 equal

Jonathan can type 20 documents in 40 minutes ,and susan can type it in 30 minutes and jack can type it in 24 minutes working together ,how much time will it is take them type the same document

If f(x) = 4x - 3 and g(x) = x + 4, find (f - g) (x)

Yvaries directly as x. y =90 when x=6. find y when x=13