The word "Substitute" means to “replace” or “put in the place of another”.
When we work out the value of algebraic expressions using substitution we replace letters with numbers.
if the expression given is; 2x-6 where x=10
Then we replace x with 10 in the expression; 2(10)-6=20-6=14
If x=4 then what is 24-5x
Solution; substitute x with 4 in 24-5(4) =24-20=4
When substituting negative numbers, put () around the numbers to get the calculations right.
Here is the rule of substitution to guide you.