Answer
Each particle has a magnitude of $200N$
Force is projected directly outwards.
Work Step by Step
Since the particles are all of equal charge magnitude, charge type, and length from each other, the force exerted will be the same for each particle.
Using Coulomb's Law:
$F = k\frac{q_{1}q_{2}}{r^{2}}$
You can calculate the force exerted on one of the particles by another. However, since there are actually two particles that are exerting a force, you actually must add up the vector components. Since the particles are in an equilateral triangle, you can take half of $60^{\circ}$ for each other particle, then take the cosine of that.
$F = (9.0x10^{9})\frac{(1.7x10^{-5})(1.7x10^{-5})}{0.15^{2}} \approx 115.6 N$
$F = cos30^{\circ}(115.6) \approx 100 N$
$ΣF = 2(100) = 200 N$
The magnitude of the total force exerted on an individual particle is 200N, and the force is directed straight outwards.