What is the derivative of sqrt7 times x +sqrt2x

I guess you mean the derivative of:

√7x + √2x, if so then:

Remember that the derivative of √u = 1/(2√u) . u'

if 7x = u, then u' = 7 , hence the derivative of √7x is 7/(2√7x)
Use same logic for √2x and you will find:

y' = 7/(2√7x) + x/√2x

Where m is the slope of the line and b is the y-intercept of the line, or the y-coordinate of the point at which the line crosses the y-axis. to write an equation in slope-intercept form, given a graph of that equation, pick two points on the line and use them to find the slope. this is the value of m in the equation.