errors

which of the following errors would cause a trial balance imbalance?

(i) the discounts received column of the cash payments book was overcast
(ii) cash paid for the purchase of office furniture was debited to general expense
(iii) return inwards were included on the credit side of the trial balance

I dont understand what is a discount received column. I understand what overcast means : means it put too much and value too high. for 2nd one, its supposed tobe dr general expense and cr cash but its dr purchases and cr cash. so its the same because both are expenses? so will still balance?