First of all for solving this question do you know the conception of : Derivatives.
and i know you can then definitely can solve the question on your own
anyhoo first we must take the derivative aka differential.
x^2+5*x
luckily this one is one of the most basic and using the rules aka formulas.
http://myhandbook.info/form_diff.html
look at constant rule, sum rule and power rule :D try it out if you can
and d/dx just means the derivative operator
so
d/dx(x^2+5*x)
means derivitve of x^2+5*x with respect to x
d/dx(x^2)+ d/dx(5*x)
the sum rule this makes it more easy :) seperated into 2 small derivatives instead of one big one. we handle it as 2 seperate problems
d/dx(x^2)= 2x
by the power rule simply decrease the exponent by 1 and multiply the variable and coefficient by the exponent you just decrased. you get 2 :).
d/dx(5*x) = 5
by factor rule
now you plug back in because you did them seperately
2x+5 and that is derivative :) with me so far?
2x+5 is also a tangent function which gives the slope of the tangent at any given x. For example at x=0 the slope is 5.
they want it at 4 tho. So plug it in
2(4)+5=8+5=13
That is your answer :)