Step-by-step explanation:
the main triangle (XYZ) and the smaller triangle (XWZ) are similar triangles.
why ? they are both right-angled (90° angle), and because the angle at X is the same for both (and the sum of all angles in any triangle is always 180°), that means that the angle XZW is the same as the angle at Y.
so, the AAA (angle - angle - angle) criteria apply.
since they are similar triangles, there is one common scaling factor (f) between pairs of corresponding lines of the triangles.
so, for the long baselines we know
25 = 24 × f
and then
7 = x × f
f = 25/24
therefore,
7 = x × 25/24
x = 24×7/25 = 168/25