Question

I am confused I want to find the values of the equation of Yi=a + bxi.

Time spent on twitter is the predictor variable and time spent working on twitter is the response
The correlation between minutes spent on twitter and minutes spent working is -0.5

The standard deviation in Twitter time is 4.86 and the standard deviation of time spent working is 3.50

I tried the following -0.5(4.86/3.50) or 4.86/3.50*-0.5 but not sure if correct way. Any one help explain this to me please.