I'm trying to study Euclidean spaces and one of the exercises is to derive the nonparametric equation for the following plane:

x = 2 - 3s + t

y = 4

z = 1 + s + t

I tried to write a new equation expressed in terms of x and y only:-

t = x - 2 + 3s = z -1 - s

However, I was stuck because I couldn't solve for s and t.

The textbook lists answer y=4 as the answer. Why? Please help me understand! Thank you!