1. If 5x + 6 = 10, what is the value of 10x + 3?

Here the question is simple.
All because, we only need to find the value of x.
We are given two equations.
5x + 6 = 10 and 10x + 3 =?
So, we will find the the value of x in the first equation, so that we can substitute the value of x in the second one and there we are with the answer.
5x + 6 = 10
For finding the value of x, all we have to do is,
Transpose the number 6 to 10
Therefore. 5x = 10 - 6 ( Take the equal sign as The Magic Bridge on which if anyone crosses it , will change its sign.)
So we have,
5x = 4
So x = 4/5 ( Multiplication will change to division after crossing the equal sign)
( Doubtful? Substitute the value of x and try!)
Now that we got the value of x,
We can just simply substitute the value of x in the second equation.
10x + 3 = ?
x = 4/5
10*4/5 +3 => 5 and 10 get canceled to 2 at the numerator.
By normal multiplication and then addition, we will get,
8 + 3 = 11
Hope this helps :)