Well, let's start from the beginning. First, you need to know how to substitute a concrete expression for a variable in another expression. Here are a few exercises. Please write the answers.
(1) Substitute 2 for x (i.e., replace x with 2) in x + 2 = 4.
(2) Substitute (3 + 5) for y in (y + 1)² = y² + 2y + 1. Don't do any simplification; just do the substitution.
(3) Let the function f(x) be defines as x + 1. Replace f with its definition in f(y + 2) + f(y + 3) = 2y + 7. Again, don't do any simplification.
(4) Let the relation R(x,y) be defines as x < y and let U(x,y) be defined as x ≤ y. Replace R and U with their definitions in "R(x,y + 1) if and only if U(x,y)."
Second, you need correct definitions.