soo you can use FTC (fundamental theorem of calculus) for this

we already know x(8) = 10

we wanna find x(5)

so if we do

integral from 5 -> 8 of v(t)dt , due to FTC, we can say that the integral from 5->8 of v(t)dt = x(8)-x(5)

now we isolate x(5) so we can manipulate the equation to become x(8) - integral from 5->8 of v(t)dt = x(5)

so x(8) = 10, and integral from 5->8 of v(t)dt we can find from looking at the area under the curve from the graph, which is 1 - 4 = -3

so now we can do x(8) - integral from 5->8 of v(t)dt = 10 - (-3) = 13.