Finite Groups

["ADH"]

a.) If G is a finite group with fewer than 100 elements and G has
subgroups of orders 10 and 25, what is the order of G?
b.) Let x and y belong to a group G. Assume x not equal to e (the
identity), |y|=2, and yxy^(-1)=x^2.  find the order of G.
I have no idea where to begin-beginner mathematician.