If a=(21) and b=(3_4) find 2a+b
AAAaannndd the bot gets it wrong yet again!
3_4 makes no sense, and 3-4 is just stupid, so I'll go with 3/4
2a+b = 2*21 + 3/4 = 42 3/4
Remember, It's not my job to figure out what you mean.
It's your job to say it so clearly you cannot be misunderstood.