Plz help im gonna cry Solve the following pairs of simultaneous equations by method of substitution.
1. x − y = 1
x + y = 3
2. y − x = 1
x + y = 5
3. y = 4x + 4
x + y = 14
4. a = 4 − b
2a + b = 1
5. 5x − 2b = 1
x = 5 − 2b
6. x − y = 4
x + 2y = 10
7. a − 2b = 1
3a − 4b = 1
8. 4x − 3y = 1
x − 2y = 4
9. a + 2p = 4
x − 2y = 6
10. 2x + 3y = 5
−x + 2y = 8
11. y − x = 2
2y − 4x = 10
12. x + 6y = 22
2x + 10y = 38
13. 2x − y = 5
x + y = 4
14. x + y = 7
2x + y = 10
15. x + y = 144
2x − 3y = 63

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?