In "Class A" define a function for your button:

def open_view_b(self):
	​# prepare fields your going to pass in context
	​ctx = {'default_x2': self.x1, 'default_y2': self.y2}
	return {
     	​	​​'name': _('Some name'),
      	​​'view_mode': 'form',
          	​'res_model': 'model of b class',
          	​'type': 'ir.actions.act_window',
          	​'target': 'current', 
          	​'context': ctx,
        ​}

You can find more info in documentation: https://www.odoo.com/documentation/16.0/developer/reference/backend/actions.html#window-actions-ir-actions-act-window