Both questions make use of the formula for the area of a triangle:
.. A = (1/2)*b*h
23. A = (1/2)*b*h
.. A = (1/2)*x*7 . . . . substitute the given values
.. A = 3.5x . . . . . . . simplified
24. A = (1/2)*b*h
.. 84.5 = (1/2)*13*h . . . . . substitute the given values
.. 2*84.5/13 = h = 13 . . . .solve for h
The height of the triangle is 13 cm.