I'm unsure how to do this problem:

(a + 2b)\nabla(\nabla \cdot \vec u) - b \nabla \times \nabla \times \vec u - (3a + 2b)c\nabla T(r)= \vec 0
\hat u = U_r \hat r + u_\theta \hat \theta +u_z \hat z
a,b,c constants
how would I solve this for u?