Multiply each term in the first group by each term in the second group using the FOIL method. FOIL stands for First Outer Inner Last, and is a method of multiplying two binomials. First, multiply the first two terms in each binomial group. Next, multiply the outer terms in each group, followed by the inner terms. Finally, multiply the last two terms in each group.

`(x * 3x+x * 10y-9y * 3x-9y * 10y) `

Simplify the FOIL expression by multiplying and combining all like terms.

`(3x^2-17xy-90y^2)`

Remove the parentheses around the expression `3x^2-17xy-90y^2`

Thus, the answer is

`3x^2-17xy-90y^2`

Find the product of `(x - 9y) (3x + 10y)` .

Multiply `(x)(3x) + (x)(10y) + (-9y)(3x) + (-9y)(10y)`

`3x^2 + 10xy - 27xy - 90y^2`

Combine like terms 10xy - 27xy.

`3x^2 -17xy - 90y^2` `lArr` **The solution.**

The product (x-9y)*(3x+10y) has to be determined.

(x-9y)(3x+10y)

= x*(3x+10y) - 9y*(3x+10y)

= 3x^2 + 10xy - 27xy - 90y^2

= 3x^2 - 17xy -90y^2

**The product (x-9y)*(3x+10y) = 3x^2 - 17xy -90y^2**