Answer:
Step-by-step explanation:
1.60
I believe that they typo meant 300 fossils of which 21% are snail shells.
Since % means per one hundred...
300(21/100)=63
Elmer has 63 fossilized snail shells.
11, rosabell had 11 posters for the parade
15. 
Add "g" on both sides

Multiply 5 on both sides to get x by itself
x = 5(a + g)
x = 5a + 5g
18. a = 3n + 1
Subtract 1 on both sides
a - 1 = 3n
Divide 3 on both sides to get n by itself
= n
21. M = T - R
Add "R" on both sides to get "T" by itself
M + R = T
24. 5p + 9c = p
Subtract "5p" on both sides
9c = p - 5p
9c = -4p
Divide 9 on both sides to get "c" by itself
c =
or c = 
27. 4y + 3x = 5
Subtract "4y" on both sides
3x = 5 - 4y
Divide 3 on both sides to get "x" by itself
x = 
x = 