exam Maths Puzzle Numerical Ability

A roofing contractor estimates that he can shingle a house in 20 hours and that his assistant can do it in 30 hours. How long will it take them to shingle the house working together? If you could explain how to do it, that would be great. Thanks.

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square root of 11(square root of 11 + x square root 22)

How do i do this kind of problem? I am lost it is

square root of 11 times square root of 11 plus x square root of 22 A straight line crosses the x-axis at x = 3 and the y-axis at y = -4. Find the equation of the line. Please give your answer in the functional form:
y = a x + b

for some constants a and b.