a small sphere of mass m carries a charge q. it hangs from a light inextensible thread of length l making an angle θ with an infinite line of charge as shown in the figure. find the linear charge density.

Whats the difficulty first find out that what are the differnt forces acting on the small sphere (i.e. electric force mg and tension making an angle theta with the vertical) then resolve it into components along x-axis and y-axis then afterwards apply the condition of equilibrium you will get the result.
Let me tell you,
As you are not provided any figure so i have assumed it by myself and gave you the explaination.
Thank You.