Answer
$|\vec{d_{1}}|\,|(\vec{d_{2}}/4)|$
Work Step by Step
Recall: $|\vec{A}\times\vec{B}|=|\vec{A}||\vec{B}|\sin\theta$
$\implies |\vec{d_{1}}\times(\vec{d_{2}}/4)|=|\vec{d_{1}}|\,|(\vec{d_{2}}/4)|\sin 90^{\circ}=|\vec{d_{1}}|\,|(\vec{d_{2}}/4)|$
