the equation usually have f(x) which means you will always put the input which is x in the ( ) if it gives you what X is put x in the (x) and whatever number is next to the ( ) you will multiply
example
f(x)= 4(x) lets say x is 3
f(3)=4(x)
=12
another example
f(x)=5(x)+12 lets say x is 2
you mutiply 5 by the number that x is given
5×2 and with that 12 you're going to add it with the problem
5×2+12 = 22
hope this helps you understand how it works
