VTMO 2017 — Grade 7 — final Question 3

After $70 \,\mathrm{km}$ at speed $v , a$ train would arrive $1 h = 20$ min late if speed were reduced $25 \%$. Traveling another $40 \,\mathrm{km}$ at $v$ before reducing gives only $1 h$ lateness. Find $v$.