“$y$,” said the student, carelessly, “$=mx+c$,” and before he knew it, his wrists and ankles were secured to the table and a laser was slowly, but extremely surely, cutting the table in two.

The Mathematical Ninja continued the lesson. “I think you mean $y - y_1 = m(x-x_1)$,” he said, patiently.

“Er… yes,” said the student. “Obviously.”

“Four-fifths!” said the student, eagerly.

The Mathematical Ninja smiled; he would have sped the laser up if the student had said 0.8. “And a point…”

”$(6,3)$!”

“Very good, so we can…”

“Substitute those in! $y - 3 = \frac45(x-6)$.”

“And then what?”

The student said “You expect me to multiply a fraction into a bracket while strapped to a table with a laser between my legs?”

The Mathematical Ninja said “No, I expect you to die.” He paused for a second. “Sorry, no. I expect you to cross-multiply. My bad.”

“Oh!” said the student. “So I can multiply the 5 onto the other side to get $5y-15 = 4x - 24$?”

Nod.

“Or… $4x - 5y - 9 = 0$?”

Nod.

“And can I get off this thing now?”

Pout. “I suppose.”

The laser stopped, and the Mathematical Ninja wondered where he was going to get a new table from.