Answer:
f2 = 140 Hz
Explanation:
let fundamental frequency is f1 = 70.0 Hz
formula for finding the higher frequency when fundamental frequency is known
fn = n f1 (where f1 is fundamental frequency and n = 1,2,3,4,5...........)
for the second frequency n=2
f2 = 2 × 70.0 Hz
f2 = 140 Hz