“Yes,” Emily said. “Write that. Not the answer. The form.”
He wrote, slowly, n = 7k + 2. His k was a little like an h. She did not correct his handwriting. Denise watched the k as if it might be sold later.
“Now the five,” Emily said. “If that number is divided by five, we want remainder three. So 7k + 2 and five have a relationship. Don’t jump. Say it.”
“Seven k plus two leaves three when you divide by five,” Caleb said. “So seven k plus two and three are kind of the same, in the world of fives. They differ by a multiple of five. I know that part. I get tangled after.”
“Then we’ll untangle in public,” Emily said. “It’s less frightening than it sounds and more frightening than a cup of coffee. Subtract two from both sides of the sameness. In the world of fives, seven k and one are the same, because three minus two is one. You have seven k leaving a remainder of one when divided by five.”