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