Number of which consumer decline and which will increase if population of frog decline all of a sudden​

see this question is based on food chain

the food chain goes like these

grasshopper-frog-snake-eagle

Explanation:

if population of frog declines suddenly population of grasshopper will decline and population of snake will increase

explanation:

given

length of train = 500 metre

speed of train = 15 metre per second in east direction

speed of bird = 10 metre per second in west direction

according to problem

=> vr = vt + vb

=> vr = 10 + 15

=> vr = 25 metre per second

now we know that

speed = distance \ time

so time = distance \ speed

=> time = 500 \ 25

=> time = 20 seconds

hence

bird will cross train in 20 seconds