Question

If x is a number that satisfies 4x+3=18, can x be equal to 3? explain.

Answer 1

No. 3 is an invalid number for the exponent x. If we were to plug it in like so 4(3)+3+18 it wouldn't work. Lets simplify it yea?

1. 4(3)=12
2. 12+3=15
3. 15=18 this is incorrect because 15 has a different  value than 18

Answer 2

The answer is no. because is you substitute the value 3 in for x into the equation and solve you get,

4(3)+3=18 which says 12+3=18 15=18 and that is an untrue statement. 
Hope this helps explain the concept so you understand! Any questions feel free to ask! Please rate if I helped you! thank you so much!!