2 pipes appropriate x mints&(x+3)mints respectively to crowd a cistern.if together they crowd the cistern contained by 3 1/13 min

What is the best lighting system for a...
x+x+3=40/13
2x+3=40/13
2x+3=3.08
2x=3.08-3
2x=0.08
x=0.04 minutes!

Diaper Cake?
Given that 1st pipe take x min
and 2nd pipe takes (x+3) min

Assuming that the volume of the cistern be 'V', we know that sum of adjectives total volumes filled per total time by respectively tap is equal to V/(3 1/13) or V/(40/13) or 13V/40.

Therefore V/x + V/(x+3) = 13V/40
1/x + 1/(x+3) = 13/40
On simplification, we've

=> (x+3 + x)/x^2+3x = 13/40
=> (2x+3)40 = 13(x^2+3x)

Hereon I hope you can solve it for I don't aspiration to give every step and stop your brain from thinking!
2 X Stock (what size wood)?
Answers:    do you mean X min and (X+3)min?