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

If jon had $4.00 then takes away $2.25, then he should have $1.75 left. $4.00 - $2.25 = $1.75 hope this ; )

That's the answer and the the information