The variable y = 7 is a solution when the RHS of equation 3y - 1 = ?  is ________. 

In an equation, the value of Left Hand Side(LHS) is always equal to the value of Right Hand Side (RHS).

Here we know the expression of LHS, we can simply calculate the value of LHS to find the value of RHS.

Putting the value y =7  in the LHS of the equation,

LHS = 3y - 1 = 3$\times$7 - 1 = 21 - 1 = 20.

We know, LHS = RHS.

$\therefore$ RHS = 20.