Robert has built a mechanical model solar system with three balls representing planets at the ends of rods attached to the center representing the sun. The planets are aligned when he
turns on the motor. The innermost planet makes a revolution in 18 seconds, the middle
planet makes a revolution in 30 seconds, and the outermost planet makes a revolution in 42
seconds. After how many seconds will the planets be aligned again?

A. 1260 seconds
B. 630 seconds
C. 315 seconds
D. 945 seconds

Okay so for every triangle has three angles that always add up to 180 degrees. and to tell the difference between whether they are secure, right or obtuse is that acute: has one angle that is less than 90 degrees. right triangle means there is at least one angle that is exactly 90 degrees. and an obtuse angle has an angle that is bigger than 180 degrees. i’ll do #13 as an example: 13. 40 and 50 so if every triangle has 180 degrees 40+50= 90 degrees then180-90= 90 degrees so the third angle is 90 degrees and because this triangle has a 90 degree angle it means it is a right triangle

The answer is