Explanation:
Next term is - 51
Use formula Tn=a+(n-1)d
a=the first term of the sequence which is - 15
d=the difference between the terms which is - 9
Substitute
Tn=-15+(n-1)(-9)
Tn=-15+9-9n
Tn=-9n-6
From this you will be able to generate all the terms in the pattern
If they say determine the 50th term just substitute 50 by n
Tn=-9(50)-6
Tn=-450-6
Tn=-456