Answer: she spent 1.42 hours practising instruments on monday
Explanation:
On Monday, Ka practiced guitar for 2 over 3 of one hour. This is 2/3 hours.
When she finished, she practiced piano for 3 over 4 of one hour. This is 3/4 hours.
The total time that Ka took in practising the guitar and piano on Monday would be the sum of the time that she spent playing the guitar and the time that she spent playing the piano. It becomes
2/3 + 3/4 = (8 + 9)/12 =17/12 = 1.42 hours.