Answer:
D. 80x + 70 = 390
Explanation:
80 times x (the degrees it heats up per minute times the number of minutes) + 70 (the degrees the oven was already at) = 390 (the number of degrees the oven needs to preheat to.)
This is the only answer that makes sense.
Hope this helps! :D
Also, where can I buy an oven that heats up this fast? XD