Lm and watts prolems. help please

Question

Find the illumination 3.8 m below a 390 lm lamp.

___lx

A screen is placed between two lamps so that they illuminate the screen equally. The first lamp emits a luminous flux of 1445 lm and is 1.9 m from the screen. What is the distance of the second lamp from the screen if the luminous flux is 2400 lm?

___m

A three-way bulb uses 50, 100, or 150 W of electrical power to deliver 665, 1620, or 2285 lm in its three settings. The bulb is placed 50 cm above a sheet of paper. If an illumination of at least 185 lx is needed on the paper, what is the minimum setting that should be used?

_______W

Answer 1

1) 1 Lux = 1 lumen per meter^2

so

390 lm / (3.8 m)^2 = 27.008 lux

2) Set up a proportion

1445 / (1.9^2) = 2400 / (x^2)

x = 2.449 m

3) Can't get it to work out right.

Hope this helps at least