dv/dt = 6t+1
{ dv ={ (6t+1) dt integrate both LHS and RHS, * { is used for integration symbol
v=3t^2 + t + c
dx/dt=3t^2 + t + c c: integral constant
{ dx= { ( 3t^2+t+c ) dt
x=t^3+0.5*t^2 +ct + d d: another integral constant
substitution
x=12,t=2
12=8+2+2c+d => 2=2c+d ------------(1)
x=34,t=3
34=27+4.5+3c+d => 2.5=3c +d ---(2)
(2)-(1)
0.5=c
substituting to (1); d=1
x=t^3+0.5*t^2+0.5t+1
t=4;
x=64+8+2+1=75m
v=3t^2 + t + c
t=4;
v=3*16+4+0.5= 52.5 ms^-1