A completes $$\frac{7}{{10}}$$of the work 15 days. Then he completes the remaining work the help of B in 4 days. The time required for A and B together to complete the entire work is = ?

• A. ${\text{8}}\frac{1}{4}{\text{days}}$$
• B. $10\frac{1}{2}{\text{days}}$$
• C. $12\frac{2}{3}{\text{days}}$$
• D. $13\frac{1}{3}{\text{days}}$$