Algebra Math Help

Please explain. -3y3 x 12 over 20 21yy2?

This is how the problem is written. negative three with a small ywith a three a line over 20 times 12 over twenty one with a ywo over a line. Do I multiplay across? Or multiply negative three y square or root which would be y three times by tweinty y two square or root y two times. I do not understand this math. The class is MAT 082 Prealgebra, by Jamie Blair, John Tobey, Jeffrey Slater. They do not explain the process of solving the math problems. I do not understand the book. Any suggestions? I have an exam on chapter 5 Tuesday July 31, 2007.
Correction there is only one y with 21 y to the 2.

Do you mean:

(-3y³ / 20) * (12y / 21)

?

That’s what I seem to be getting from your description, although I can’t make sense of the title.

So let’s start with this problem:

(-3y³ / 20) * (12y / 21)

This is the same as

(-3y³)(12y) / (20)(21)

Multiplying this out, followng the order of operations gives you:

(-36y^4) / 420

because 12 times negative 3 equals negative 36, y^3 times y equals y^4, and 20 times 21 equals 420.

Note when multiplying exponents:

(y²)(y³) = y^(2+3) = y^5, so likewise with

(y³)(y¹) = y^(3+1) = y^4

However, if it was an exponent raised to an exponent, like this:

(y³)²

You would multiply the exponents, and so this would equal

(y³)² = y^(3*2) = y^6.

Because 36/420 reduces to 3/35, you get

(-3y^4 / 35).