What exactly do you want to know? The first thing the problem says is "in the absence of species Y (i.e. y= 0)" so the two equations become

and 0= 0. (The right side of the second equation is 0 because it is 0 times something. The left hand is 0 because y is a

**constant**, 0, and the derivative of a constant function is 0.)

That equation is a "separable first order equation" which is typically the first thing you study in differential equations. You can "separate" it as

Integrate on the left using "partial fractions".