The number of seats in the first 12 rows of a high school auditorium form an arithmetic sequence the first row has 9 seats the second row has 11 seats. a) write a recursive formula to represent the sequence b) write an explicit formula to represent the sequence. c) how many seats are in the 12th row. plz me asap it's a math question not chemistry

A) The recursive formula for the number of seats in the n th row will be; 
S1 = 9
S(n) = S (n-1) +2 

b) Explicit formula; is that of an arithmetic progression; such that if a is the first term , and d is the common difference , then the n th term will be given by the formula:  a + (n-1) d; where a is 9, and d is 2
Hence; for n th row = 9+ 2(n-1)

c) Number of seats in 12 th row using the formula in b.
 n = 12 , a = 9, d = 2
therefore; 9 + 2(12-1)
              = 9 + 2(11)
              = 31 seats 

Ch4 and ph3 are both covalent since they are composed both of non-metals.    ch4 is non- polar because of  london forces and has a geometry of tetrahedral  ph3 , on the other hand, is umbrella shaped polar and has dipole-dipole intermolecular force (imf) . since ph3 is polar, it has a stronger imf