Linear endomorphism of a vector space of matrices

Let M4(R) denote the 16-dimensional real vector space of 4×4 matrices with real entries, in which the vectors are represented as matrices. Let T:M4(R)→M4(R) be the linear transformation defined by T(A)=A−A⊤.
(a) Determine the dimension of ker(T).
(b) Determine the dimension of im(T).