Tangent to the y-axis means that it just touches the y-axis. This is the equation of the circle you desire, (x+5)^2+(y+2)^2=25. You get this because you want the length of the segment that goes from the point (-5,-2) to the y-axis. This will end up being your radius. Notice (-5,-2) lies on the line y=-2, so you wish to use the distance formula or by simply just looking at it geometrically answer this, how many units do you need to add to -5 to get to 0.....5 right? And remember its always radius^2, hence the 25. Message me if anything is confusing.