You can set up a ratio:
[tex] \frac{object weight on A}{object weight on B} = \frac{elephant weight on A}{elephant weight on B}[/tex]
By substituting in the numbers, you get:
[tex]\frac{100}{3} = \frac{2900}{x}[/tex]
[tex](\frac{100}{3}) * x = (\frac{2900}{x}) * x [/tex]
[tex]\frac{100x}{3} = 2900 \\ (\frac{100x}{3}) * 3 = 2900 * 3[/tex]
100x = 8700
100x / 100 = 8700 / 100
x = 87 pounds
Hope this helps! :)
