#180°:pi=()°:(rad)#. Set #(rad)=2.5# and solve for #()°# degrees.

Explanation:

You probably know that #180°# corresponds to #pi# radians;
You can build the proportion: #180°:pi=()°:(rad)#
Set #(rad)=2.5# and solve for #()°# degrees;
you'll get: #()°=180°2.5*1/(pi)=180°2.5*1/(3.14)=143.3°#