Linear Regression??

So I'm a little clueless with this I feel like I don't have enough information but maybe I'm missing something. Here is the question:

Assume that Rxy is .40. Write the least-squares linear regresssion equation for predicting Y based on X.

I did this in a previous question but it had a complete data set and I did not use Rxy so how do I formulate it with only that??

The only other thing I have is the second part of the question which says : then, use the regression equation to predict Zy for a person whose Zx is 1.50

That didn't seem to me like it would help much for the first part.