nomer 5 sm 6 please...

A) Dik :
QR = 20
TS = 15
SP = 18

Dit : RS?
20 / 18 + RS = 15 / 18
20 × 18 = 15 × (18 + RS)
360 = 270 + 15RS
360 - 270 = 15RS
90 = 15RS
90 / 15 = RS
6 = RS