model methods and admin.py

Using Django The Admin
7

Model

class GateSale(models.Model):
    combinedGateProfit = models.DecimalField('Combined Gate Profit', null=True, blank=True, max_digits= 8, decimal_places=2)
    fiftyFiftyTotal = models.DecimalField('Fifty-Fifty Total', null=True, blank=True, max_digits= 8, decimal_places=2)
    officialsTotal = models.DecimalField('Officials', null=True, blank=True, max_digits= 8, decimal_places=2)

    @admin.display(description='gameProfit')
    def gameProfit(self):
        gameProfit = (GateSale.combinedGateProfit + (GateSale.fiftyFiftyTotal/2)) - GateSale.officialsTotal
        
        return '%d' % (gameProfit)

Admin

from .models import GateSale

@admin.register(GateSale)
class GateSaleAdmin(admin.ModelAdmin):
    list_display = (
        'gameProfit'
        )

Error

TypeError at /admin/website/gatesale/
unsupported operand type(s) for /: 'DeferredAttribute' and 'int'