Answer:
x=21
Explanation:
We know that the angles of a triangle has a sum of 180 degrees always. We know two sides already which are 45 and 63. Their sum is 108 degrees which means that the missing side is 180-108 which is 72.
Now we can set 72 equal to 4x-12 since the last side has to equal 72 and solve.
72=4x-12
84=4x
x=21
Hope this helps!!!