In problems of probability, it is best to find out the sample space or all the possible outcomes from throwing 3 coins in the air.
S = {HHH, TTT, HHT....}
The condition is at least 2 landed on heads (that means 2 or more). From the sample space, that can only be {THH, HHT, HTH, and HHH}.
Therefore, the probability is 3/4 since there are a total of 8 possible outcomes.