Could someone explain to me how this problem is done?

Goodness and fit test

1. Consider rolling a die. Suppose the die is rolled 120 times and each result is recorded. Theoretically, if the die is balanced, we would expect each face to occur 20 times. The results are given in the table. When comparing the observed frequencies with the corresponding expected frequencies, we must decide whether it is possible that these discrepancies occur as a result of sampling fluctuations and that the die is balanced or that it is not legal and that the distribution of results is not uniform.

Using a significance level of 0.05

2 3 4 5 6 Observed 20 22 17 18 19 24 Expected 20 20 20 20 20 20