Find the distance traveled on the velocity-time graph

[chwala]

Homework Statement

part b. find the distance travelled in the first $50$ seconds

Relevant Equations

kinematics

now this is my approach, my interest in on part b
distance travelled= area under the graph between time $t=0$ and $t=50$,
area = $0.5(40+20)10+ (20 × 40) + 0.5(40+20)10+ 0.5×10×20$
Area= $300+800+300+100=1500m$
now textbook says i am wrong, where have i made a mistake?

 

[chwala]

aaaargh i have seen the mistake...

 

[chwala]

area = $0.5(50+20)10+ (20 × 50) + 0.5(50+25)10+ 0.5×10×25$
Area= $350+1000+375+125=1850m$