No you have to make sure to line up the decimals when subtracting them. Do not just line of the numbers, this wills get you the wrong answers. Hope this helps. If you need anything else just call for a helping hand.
Answer:
There are 16 Oak tree in the forest.
Step-by-step explanation:
Given: There are 4 Oak tree on every 10 pine trees.
There are total 24 more pine tree than Oak tree.
Using the ratio of trees to find the number of trees.
Lets assume there are total number of Oak tree be "x".
∴ Total number of Pine trees will be 
We know the ratio of Oak to Pine tree is 4:10 or 
⇒
Multiplying both side by 
⇒ 
Using distributive property of multiplication, distributing 4 with x and 24.
⇒ 
Multiplying both side by 10
⇒ 
subtracting both side by 4x
⇒ 
dividing both side by 6
⇒
∴ 
Hence, There are 16 Oak trees in the forest.
Simplifying
8a + 12b = 92
Solving
8a + 12b = 92
Solving for variable 'a'.
Move all terms containing a to the left, all other terms to the right.
Add '-12b' to each side of the equation.
8a + 12b + -12b = 92 + -12b
Combine like terms: 12b + -12b = 0
8a + 0 = 92 + -12b
8a = 92 + -12b
Divide each side by '8'.
a = 11.5 + -1.5b
Simplifying
a = 11.5 + -1.5b

Explanation:
As we know that set is the collection of elements and set builder is the method of defining the set with the help of specific property in which we can use arithmetic operations as well
Generally,
It is the general form of any set in which we can construct the complete set with the help of equation in the given in set builder form.
Since we have the elements : 45,55,65,75
So, the set builder form will be { x: x =5(2n+1) ,4≤n≤7,x,n∈ N }
We will read it as it is the value of x which will be find with the help of given equation i.e. x=5(2n+1) where n goes from 4 to 7 only and x and n are natural numbers only.