José, vecino de mi calle, me ofrece $3840 por mi computadora, con lo que ganaría el 28% del costo. siete días después se la vendí a rogelio, compañero de grupo, en $3750, ¿qué porcentaje del costo gané al hacer la venta? cual el procedimiento que operaciones se realizaron

The first thing we must do for this case is to determine the cost.
 For this, we make the following rule of three:
 3840 > 128%
 x > 100%
 Clearing x we have:
 x = (100/128) * (3840)
 x = 3000
 We now look for the percentage earned when making the sale.
 For this we make the following rule of three:
 3000 > 100%
 3750 > x
 Clearing x we have:
 x = (3750/3000) * (100)
 x = 125
 Then, the percentage earned is:
 125-100 = 25%
 
 I won 25% of the cost when making the sale.

The american colonies would have been ruled by a king.