Explanation:

Let x, y and z are the one day’s work of Trump, Putin and Jinping respectively.
According to the question,
⇒ 3 × (x + y + z) = 37% of the work
⇒ 7 × (x + y) = 63%
⇒ x + y = 9%
? The ratio of efficiency of Trump and Putin is 4 : 5,
∴ 5x = 4y and x = 4%, y = 5% work per day.
It implies Trump can complete the job and in 25 days and Putin in 20 days.
In 3 days (x + y + z) do 37% of the work
Out of this Trump and Putin would do 27% work = (3 × 9%) of the work.
Remaining work = 37% – 27% = 10% (done by Jinping in 3 days)
∴ The work of z = 10/3 = 3.33% work per day
∴ Jinping is the slowest and he would do the work in 30 days.