The length of the hypotenuse, line segment ac, in right triangle abc is 25cm. the length of line segment is 15cm. which is a approximate measure of angle acb

According to the Pythagorean Theorem,
hypotenuse^2 = leg^2 + leg^2
25^2 = 15^2 + leg^2
625 - 225 = leg^2
leg = 20
Since there is NO diagram, I am guessing at what angle ACB is.
sine(ACB) = 20 / 25 = .8
arc sine (.8) = 53.13 degrees

In case it should be the other angle, then it is
36.87 degrees

No a triangle cannot be formed because when you add the two smallest number together (which would be 11) the have to be bigger than the number it is "against" ( which would be 12)