Suppose that in a certain triangle, the degree measures of the exterior angles are in the ratio 2: 3: 4. if the largest interior angle measures y degrees, what is the value of y?

First you should calculate total of the ratios:
2+3+4=9
then divide 360 by 9 (because the total degrees of the exterior angles in polygon is 360)

at the end find the amount of the exterior angles:

the shortest exterior angle is 80 degrees
so it has the largest interior angle:
180-80=100
the answer is 100