Not sure for (b)
Step-by-step explanation:
(a)55+80+x=180 (angles inside the triangle)
135+×=+180
x=180-135
x=45
A
this is a geometric sequence since there exists a common ratio r between the terms
r =
=
=
= 3
B
to obtain the next term in the sequence multiply the previous term by 3
= 3
← recursive rule
C
the n th term of a geometric sequence is
=

where
is the first term in the sequence
= 7 ×
← explicit rule