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The solution by @josgarithmetic is a b s o l u t e l y w r o n g and t o t a l l y i r r e l e v a n t.
For your safety simply ignore it.
I came to bring the correct solution - see below.
1. First, the lateral surface area of the given pyramid is = 336 - 144 = 192 square inches.
2. The lateral surface area consists of 4 congruent triangles - so the area of each triangle is = 48 square inches.
3. The base of each such a triangle is 12 inches; hence, the slant height of the pyramid is = 8 inches.
4. Then the height of the pyramid is = = = = units. ANSWER
Solved.