Thread: Proportion problem

I'm stuck to a proportion problem: A tree which is known to be 75feet high stands on one bank of a river at the waters edge and casts a shadow which just reaches straight across to the other bank, and at the same time a yard stick casts a 4foot shadow. Find the width of the river. Please help, thank you!

The tree is as many times taller than the yard stick as the tree's shadow (i.e., the river width) is longer than the yard stick's shadow.

Thank you emakarov!

I can't figure it out... how do I write it algebraically?