First add up the total parts in the ratio.
5 + 4 = 9
Now we need to know the value of each part
36 / 9 = 4
The girls has total of 4 parts, therefore we can just multiply the number of parts by the amount in each part
4 x 4 = 16
So there r 16 girls in the class
7v = 2v - 20
First, subtract 2v from both sides. / Your problem should look like: 7v - 2v = -20
Second, simplify 7v - 2v to 5v. / Your problem should look like: 5v = -20
Third, divide both sides by 5. / Your problem should look like: v =
Fourth, simplify

to 4. / Your problem should look like: v = -4
Answer:
v = -4
You should use Order of Operations or PEDMAS for this (Parenthesis, Exponents, Division and Multiplication in the order they appear, Addition and Subtraction in the order they appear). So we do the 2+12 because that is in parentheses first which gives 14-3+6. Next we do 14-3 because there are no exponents and no division or multiplication, which gives 11+6. This yields your answer, 17.
Answer is 15%
You have to do a proportion
12. = x
80 100 and u have to cross multiply
80x = 1200
80. 80
then divide 1200÷80=15