Using forward finite difference scheme to find first and second derivative given data points

Im struggling to figure out how to code this. If i had the data points

time(f)=[0,2,4,6,8,10,12,14,16]; position(f(t))=[0,0.7,1.8,3.4,5.3,6.2,7.3,8,8.4]; and h=2 using forward finite difference equations dfdx=f(i+1)-f(i)/h; dfdx2=f(i+2)-2*f(i+1)+f(i)/h^2;

how would I code it so that when I wanted to know the derivative at a user entered time for example at t=10 (which would be i=6) it would run for the first derivative using the equation dfdx=f(i+1)-f(i)/h;

dfdx=7.3-6.2/2 =0.55

not sure how to implement the finite equations to calculate this for any t that is entered. Just looking for a simple way to to this. Thank you!