smc

It must be assumed that the pipes have an equal height. We can represent the amount of water carried per unit time by cross sectional area. Cross sectional of Pipe with diameter $6in$, $$\pi r^2=\pi \cdot 3^2=9\pi$$ Cross sectional area of pipe with diameter $1in$ $$\pi r^2=\pi \cdot 0.5\cdot 0.5=\frac{\pi }{4}$$ So number of 1 in pipes required is the number obtained by dividing their cross sectional areas $$\frac{9\pi }{\frac{\pi }{4}}=36$$ So the answer is $\boxed{36}$.