Can anyone me with these two questions ?

That top one is a geometric sequence because it has a common ratio.  The common ratio is just a constant multiple that exists between any term and the previous one.  In this case it is:

-44/88=22/-44=r=-1/2

Any geometric sequence can be expressed as:

a(n)=ar^(n-1), a=initial term, r=common ratio, n=term number, in this case:

a=88 and d=-1/2 so

a(n)=88(-1/2)^(n-1) so the fourth and fifth terms are:

a(4)=88(-1/2)^(3)=-11, a(5)=88(-1/2)^4=5.5



Again, this is a geometric sequence because there is a common ratio, r of:

16.8/42=6.72/16.8=r=0.4 or if you prefer 4/10, and a=42 so the rule is:

a(n)=42(4/10)^(n-1) so the fourth term is:

a(4)=42(4/10)^3=2.688