∆ QSV is similar to ∆ RST by SAS similarity postulate
Similar triangles are triangles with equal corresponding angles and equal side ratio i.e the ratio of their corresponding sides are equal.
To prove that ∆QSV is similar to ∆RST
angle QSV is congruent to angle RST
Calculating VS
12/x = 3/5
60 = 3x
x = 20
VS/TS = RT/QV
Therefore, QSV is similar to ∆ RST by SAS similarity postulate