Jerry and Marcus will usually both run 5 miles each time they go running. This month, Jerry ran an additional 18 miles. Which answer choice shows an expression that represents the total distance Jerry and Marcus ran this month if j = the number of times that Jerry ran and m = the number of times that Marcus ran?

You can use the C. HL Theorem to prove the triangles congruent.

To use the HL THeorem to prove the triangles congruent, you have to check for three conditions. 
1) The triangles are both right triangles.
2) Their hypotenuses are congruent
3) They have one pair of congruent legs.

The squares at the angle of the triangle indicate the triangles are right triangles. Since the triangles in the picture share one side, the hypotenuse, the hypotenuses of the triangles are congruent. The triangles also have one pair of congruent legs. Since all three conditions of the HL Theorem are met, the triangles are congruent.