Answer:
AD=175.66 units
Step-by-step explanation:
It is given that ABC is an isosceles triangle in which base is 246 and the non base angle is 70°.
Thus, applying the angle sum property in ΔABC, we get
∠A+∠B+∠C=180°
⇒70°+2∠B=180°
⇒∠B=55°
Thus, ∠B=∠C=55°.
Now, Draw AD perpendicular to BC such that BD=DC=123, then applying trigonometry in ΔADC, we have

⇒
⇒
⇒
Thus, the length of the altitude is 175.66.