The cost of producing a number of items x is given by

C = mx + b, in which b is the fixed cost and m is the variable cost (the cost of producing one more item).
(a) If the fixed cost is $40 and the variable cost is $10, write the cost equation.
(b) Graph the cost equation.
(c) The revenue generated from the sale of x items is given by R = 50x. Graph the
revenue equation on the same set of axes as the cost equation.
(d) How many items must be produced for the revenue to equal the cost (the
break-even point)?

what is your question? a) is just plug the numbers in for m,b. b) is graph it.
c) is graph a new equation on the same graph.
d) is where the lines cross.

You will have to draw your own graphs. We can't do it for you here.

(a) Cost: C = 10 x + 40 (in dollars)

(c) Revenue: R = 50 x

(d) Look for the point on your graph were the C and R lines intersect. That will be the breakeven point.

It will also be where 10 x + 40 = 50 x