The cost of making 4 lamps is $370. The cost of making 11 lamps is $755.
What is the cost per lamp?

Whenever you have a ratio or quotient of two things, you have to think of the division sign as “per.” It helps so much when dealing with calculus problems, if you ever want to pursue that.

So these two sentences are basically saying “it is $370 per 4 lamps” and “it is $755 per 11 lamps.” So if you want the amount of dollars per 1 lamp, divide by the denominator.
370/4 = $92.50 per lamp
$755/11 = $68.64 per lamp