Well to find this first you will divide the area by the length.
If you can use a calculator just put 11.875/4.75 which gives you as your width 2.5.
If you can't then change them into irregular fractions so...
11 7/8 --> 95/8
4 3/4 --> 19/4
Then divide them
95/8 / 19/4
95/8 * 4/19
380/152= 2.5 or 2 1/2
