(b) Rs 12,398.40
Let Mrs. Sharma’s monthly salary be Rs x. Then, 15% of x = Rs 4428
\(\Rightarrow\) x = Rs \(\frac{4428\times 100}{15}\) = Rs 29520
\(\therefore\) Total monthly amount invested by Mrs. Sharma = (15% + 18% + 9%) of Rs 29520
= 42% of Rs 29250 = \(\frac{42}{100}\) x 29250
= Rs 12398.40.