I have the following ellipse : $\frac{(x-3)^2}{\frac{9}{4}} + \frac{(y+4)^2}{\frac{25}{4}}=1$

In this case, b > a. It says that to find the eccentricity I must use $\frac{c}{a}$ but I think this is only valid when a>b. What'S the formula to find the eccentricity in my case ?