ETAPA 1Escolha a opção correta
ETAPA 2Adicione exercícios que você gosta aos Favoritos
Use for if the actual sum is mentioned, use at if the actual sum isn't given.
If the weight or measure follows the price, use at with the actual sum: That velvet is available at £5 a metre.
Don't use for in the sense of about. The chief use of for is to convey the idea of being in favour of. If we say that the teacher spoke for bad habits it's like saying that he/she spoke in favour of bad habits!
Use to to express motion from one place to another, use at to denote position.