4 questions math stuck need help

9.) no she will not have enough money because 6(6)+ 5= 41 which is more than the 35 dollars she has. She will need 6 more dollars
10.) to make a profit of 20 dollars, add 20+40 then divide by the number of notebooks, 30, to get the price per notebook to get a profit. It is $2 per notebook.
11.)the perimeter is calculated by 2*length + 2*width so 12x + 6x + 10. This is all going to be equal to 185 so the equation to solve for x is 18x + 10= 185. Subtract 10 from 185 to get 18x =175. Then divide 175 by 18 to get x= 9.7222
12.) put 15 in for the value of x in the equation 6.85+ 0.65x to get 6.85+ 9.75 and a total of $16.60

Could you make it more clear?