This is another question I can't figure out.

Question

Given planes pie1 and pie2 defined as:

pie1: 2x + 5y - 7x + 2 = 0
pie2: x + y - z + 3 = 0

(b) Give the equation of the line of intersection of these two planes.

I only found the answer for (a) where they ask to find the angle between both planes.

Thank you!