To find 'd' choose one calculation:

Answer:
[tex]\sqrt{7^{2}+5^{2} }[/tex]
Step-by-step explanation:
Since the whole base of the triangle is 14, we can half it to find the base of one triangle which is 7.
Pythagoras Theorem states a² + b² = c²
In this case a² = 7 and b² = 5 so,
a² + b² = c²
a² = 7 and b² = 5
7² + 5² = c²
49 + 25 = c²
74 = c²
√74 = c