The answer will be d but I am not fully sure.
Given:
y is directly proportional to x.
when 
To find:
The equation that connects y with x.
Solution:
It is given that, y is directly proportional to x. So,

...(i)
Where, k is the constant of proportionality.
We have,
when
. Substituting these values in (i), we get
Divide both sides by 5.
Substituting
in (i), we get
Therefore, the required equation is
.
Answer:
L = 48
Step-by-step explanation:
Given that L varies directly with Z² , then the equation relating them is
L = kZ² ← k is the constant of variation
To find k use the condition L = 12 when Z = 2 , then
12 = k × 2² = 4k ( divide both sides by 4 )
3 = k
L = 3Z² ← equation of variation
When Z = 4 , then
L = 3 × 4² = 3 × 16 = 48