The expression ax + by has value 7 when x = 2 and y = 1. When x = -1, y = 1, it has value 1, find a and b.

Can the following equations hold simultaneously?

3x - 7y = 7

11x + 5y = 87

5x + 4y = 43.

If so, find x and y.

Solve the following systems of simultaneous linear equations by cross-multiplication method :

3x - 7y + 10 = 0

y - 2x = 3

Solve the following system of simultaneous linear equations by cross - multiplication method :

2x - 5y = -1

3x + y = 7