Answer
The electric force on the charged particle will be $1.5~F$
Work Step by Step
We can write an expression for the original electric force on the charged particle:
$F = E~q$
We can write an expression for the new electric force on the charged particle:
$F' = (\frac{E}{2})~(3q)$
$F' = 1.5~E~q$
$F' = 1.5 ~F$
The electric force on the charged particle will be $1.5~F$.
