A projectile is projected at angle of projection $60 ^ { \circ }$ with speed $u$. When its velocity makes an angle $45 ^ { \circ }$ with horizontal its speed is $20 \mathrm {~m} / \mathrm { s }$. Find u ?
(A) $\mathbf { 1 0 } \sqrt { \mathbf { 2 } }$
(B) $20 \mathrm {~m} / \mathrm { s }$
(C) $20 \sqrt { 2 } \mathrm {~m} / \mathrm { s }$
(D) $40 \mathrm {~m} / \mathrm { s }$