<span>System 1 and system 3, because the second equation in system 3 is
obtained by adding the first equation in system 1 to three times the
second equation in system 1.</span>

**Answer:**

78.70

**Step-by-step explanation:**

This is impossible to answer without the scatterplot. Look at the point where the person scored 81, from there "draw" a straight line down to the bottom line, where it should answer how long the student studied for.

40/8 , 50-5 , 8+20+35 , 17+x , 1/2 1p , k-2

∠C = 180° - 45° - 65°

∠C = 70°

b/sin B = c/sin C

b/sin 65° = c/sin 70°

b = c/sin 70° × sin 65°

b = 20/0.9397 × 0.9063

b = 19.289

**b = 19.3**