Which of the following lengths will form a triangle? A: 12.6 cm, 5.4 cm, 5.4 cm
B: 7.2 cm, 5.9 cm, 1.3 cm
C: 11.5 cm, 4.2 cm, 7.6 cm
D: 3.1 cm, 6.6 cm. 10.4 cm​

If you have the following equation, 2/3x+5/6-x=2-3/4x what would you multiply each term by to get rid of all the fractions

Having a hard time understanding this question (see attachment).

Aspacecraft can attain a stable orbit 300 kilometers above earth if it reaches a velocity of 7.7 kilometers per second. the formula for a rocket's maximum velocity v in kilometers per second is vequalsminus0.0098tplusc ln upper r, where t is the firing time in seconds, c is the velocity of the exhaust in kilometers per second, and r is the ratio of the mass of the rocket filled with fuel to the mass of the rocket without fuel. find the velocity of a spacecraft whose booster rocket has a mass ratio of 20, an exhaust velocity of 2.1 km/s, and a firing time of 15 s. can the spacecraft achieve a stable orbit 300 km above earth?