Hi,
Hashrates 21Mh/s - 25Mh/s that you say is for "Ethash" algorithm (ETH, ETC) only.
But algorithm of Monero is "CryptoNightV8" that RX 470 can give you only 660 hash/s in this algorithm.
So if you buy 2x RX 470 then you have 1320 hash/s in "CryptoNightV8" algorithm and based on link below, you can get only $3 a week
https://whattomine.com/coins/101-xmr-cryptonightv8?utf8=%E2%9C%93&hr=1320&p=300&fee=1&cost=0.3&hcost=0.0&commit=Calculate
Mining is not profitable anymore, I suggest you to invest in Cryptos instead of buying GPUs.
Hashrates 21Mh/s - 25Mh/s that you say is for "Ethash" algorithm (ETH, ETC) only.
But algorithm of Monero is "CryptoNightV8" that RX 470 can give you only 660 hash/s in this algorithm.
So if you buy 2x RX 470 then you have 1320 hash/s in "CryptoNightV8" algorithm and based on link below, you can get only $3 a week
https://whattomine.com/coins/101-xmr-cryptonightv8?utf8=%E2%9C%93&hr=1320&p=300&fee=1&cost=0.3&hcost=0.0&commit=Calculate
Mining is not profitable anymore, I suggest you to invest in Cryptos instead of buying GPUs.