Answer:
5/9÷⅓
reciprocate ⅓ into 3/1
=5/9×3/1
=15/9
simplify
=5/3
The answers are
D --> Boron family
H --> Halogens
A --> Alkali metals
I --> Noble gases
Hope this helps
d1 = 51(t)
d2 = 71(8 - t)
d1 + d2 = 508
and now you just have to solve for t.