input: Write a python function to solve linear equations of the form "ax + b = c".
  assert solve("2x + 3 = 5") == 1.0
  assert solve("3x + 4 = 10") == 2.0
  assert solve("5x + 6 = 21") == 3.0
output: def solve(equation):
      equation = equation.replace(" ", "")
      lhs, rhs = equation.split('=')
      a, bx = lhs.split('x')
      a = float(a)
      b = float(bx)
      c = float(rhs)
      x = (c - b) / a
      return x