Like terms:
1.4c, -2c, -7.3c
11.4 has no like terms
Step-by-step explanation:
the formula for the sum of the first n terms of a geometric sequence is
Sn = s1(1 - r^n)/(1 - r)
with r being the common ratio and s1 is the first term.
so,
S15 = 7×(1 - (-3)¹⁵)/(1 - -3) = 7×(1 - -14,348,907)/4 =
= 7×14,348,908/4 = 7×3,587,227 = 25,110,589
Total amount of Carbon-14



=C
Full marks answer
1,387 because you just add all the bricks (421+623+343)
Explanation is in the file
tinyurl.com/wpazsebu