I need help...

Did I end up with the correct answer?

A trapezoid has equal nonparallel sides, The upper base is 6, the lower base is 16 ( 11,5) and the diagonal is 12. What is the altitude of the trapezoid? Round your answer to the one decimal place.

I was told this is how to get the
answer.
h(squared)+ 11(sqared)=12(squared)

___I worked it out___
12(squared)-11(sqared)= 23
sqare root of 23 is 4.8
=4.8
Is this right?

Yes, it is correct. Drop a verical line from an upper correr perpendicualr to the base. The diagonal, h and 8+3 = 11 form a right triangle.