RUBUSD - how many RUB per USD
TRYUSD - how many TRY per USD
RUBTRY - how many RUB per TRY
RUBUSD/TRYUSD = RUBTRY
64.42/4.48 = 14.3795 which is less RUB per TRY compared to the direct RUBTRY quote.
Use your USD to get TRY - gives 4.48M
Use TRY to get RUB - gives 64.4672M
Use RUB to buy USD - gives ~ 1.000.732,692 USD
If you are unsure about the direction, you can simply try going around the circle in either direction. One way you will end up with a profit, the other with a loss.
There will be numerous online resources for questions like this if you spend some time with google. Searching cross triangle arbitrage should show Investopedia's Triangular Arbitrage Definition - Investopedia as the first result. This page also has a working example with EUR / GBP and USD:
EUR/USD = 0.8631, EUR/GBP = 1.4600 and USD/GBP = 1.6939.
With these exchange rates there is an arbitrage opportunity:
Sell dollars for euros: $1 million x 0.8631 = €863,100
Sell euros for pounds: €863,100 ÷ 1.4600 = £591,164.40
Sell pounds for dollars: £591,164.40 x 1.6939 = $1,001,373
Subtract the initial investment from the final amount: $1,001,373 – $1,000,000 = $1,373
From these transactions, you would receive an arbitrage profit of $1,373 (assuming no transaction costs or taxes).