I wrote out the steps on the attached slide. I hope I'm able to help you, Sweetie.
ANSWER
The coefficient is 70.
EXPLANATION
The given binomial expression is

The specific term of a binomial expansion can be determined using the formula,

where

We substitute these values into the formula to get,

We simplify to get,

Hence the coefficient is 70.
You can do 5+5+10, 6+6+8, 9+9+2, 4+4+12, 3+3+14, 2+2+16, 1+1+18. I believe these are all of them, so there are 7 ways.
It is 50,000 less
450 x 100 = 450,000