Let's work through the two parts of the problem.

a) Find the value of $1 + 3x$ when $x = 1$:

We simply substitute $x = 1$ into the expression: $1 + 3x = 1 + 3(1) = 1 + 3 = 4$ So, the value is 4.

b) Find the value of $7 - 2x$ when $x = -3$:

Again, substitute $x = -3$ into the expression: $7 - 2x = 7 - 2(-3) = 7 + 6 = 13$ So, the value is 13.

Would you like further details or explanations?

Here are five follow-up questions:

1. What is the result of $2x + 5$ when $x = 4$?
2. How does the value of $1 + 3x$ change if $x = -2$?
3. What happens to $7 - 2x$ when $x = 0$?
4. How do you evaluate expressions with negative values of $x$?
5. What is the process for solving for $x$ in more complex expressions?

Tip: Always substitute carefully and simplify the expression step-by-step to avoid mistakes.