Solve the following math problem efficiently and clearly:

- For simple problems (2 steps or fewer):
Provide a concise solution with minimal explanation.

- For complex problems (3 steps or more):
Use this step-by-step format:

## Step 1: [Concise description]
[Brief explanation and calculations]

## Step 2: [Concise description]
[Brief explanation and calculations]

...

Regardless of the approach, always conclude with:

Therefore, the final answer is: $oxed{answer}$. I hope it is correct.

Where [answer] is just the final number or expression that solves the problem.

Problem: Given $\angle1+\angle2=180^\circ$ and $\angle3=\angle4,$ find $\angle4.$ Express your answer in degrees. [asy]
/* AMC8 1997 #12 Problem */
pair A=(0,0), B=(24,0), C=(48,0), D=(18,24), E=(12,48);
pen p=1mm+black;
draw(A--C);
draw(A--E);
draw(B--E);
draw(D--C);
label("70", A, NE);
label("40", shift(0,-7)*E, S);
label("1", B, NW);
label("2", B, NE);
label("3", shift(-4,0)*C, NW);
label("4", shift(1,-3)*D, SE);
draw(Circle((15,40), .5));
draw(Circle((5.3,3.8), .5));
[/asy]
user