For most of these, Wolfram Vertical Line Alpha seems to give reasonable results. However, for the third one, because I'm in Argentina, it helpfully converts US$79.80 into Argentine pesos, getting an answer that's off by about a factor of 2: AR$7969.44. As https://preciodolarblue.com.ar/ explains, the current bid and ask prices for the dollar are AR$195 and AR$199. Wolfram Vertical Line Alpha is apparently using the "official" rate of AR$99.45 or so; this is the rate at which the government converts your dollars into pesos if you are an exporter, but you cannot convert your pesos into dollars at this rate without special permission, granted, for example, if you are going on vacation to Disney World.