Is it 1 solution, no solution or infinite solution? -28 = -7(3x + 4) + 21

The serenity and the mystic are sail boats. the serenity and the mystic start at the same point and travel away from each other in opposite directions. the serenity travels at 16 mph and the mystic travels at 19 mph. how far apart will they be in 3 hours?

What is the common difference for this arithmetic sequence? -6,-2,2,6,10 a.4 b.5 c.3 d.6

What are the solutions for the following system? -2x^2+y=-5 y=-3x^2+5