How do the magnitude and charge of the two charged particles in the figure above compare?

The figure shows the charges a and b and the electric field lines around them.

The lines shown correspond to the electric field created by two charges of the same magnitude and of the same sign (positive because the lines are pointing outwards the charges).

The relative magnitude of the charges is indicated by the proximity of the lines.

These are the considerations that lead to the

1) Lines leaving away from the charge mean that the charge is positive. Which is the case for the both a and b charges.

2) The proximity/separation (density of the lines) is used to indicate relative magnitude. Given that the proximity of the lines generated by the charge a is equal to the proximity of the lines generated by the charge b, the magnitudes are the same.

Conclusion: they are two positive charges of same magnitude.