7.8 should be it, i am so sorry if its wrong hope it helps if its correct!
R(t) = 4t
A(r) = π(r^2)
a) A(t) = A[r(t)] = π[r(t)]^2 = π[4t]^2 = 16π(t^2)
b) t = 4,
A(4) = 16*3.14*(16)^2 = 12,861.44
Your answer is the last one!
The ratio of pop songs to rock songs you download is 5:4, and 40 are pop songs. You want to find out how many rock songs there are.
First, add the ratios together: 5+4=9. This means that 9 will be your denominator, so 5/9 songs are pop and 4/9 songs are rock.
Now you know that pop songs account for 5/9 of the songs, this means that 40 is 5/9 of the total songs.
To find out how much 4/9 is, you need to divide 40 by 5 to get 1/9 and times that number by 4 to get 4/9:
40÷5=8×4=32 songs are rock songs
