Last Thursday, John assembled chairs at a rate of 3 chairs per hour for part of the day and Larry assembled no chairs. Last Friday, Larry assembled chairs at a rate of 4 chairs per hour for part of the day and John assembled no chairs. If John and Larry assembled chairs for a total of 7 hours during these two days, how many chairs did John assemble last Thursday?

Answer:9 chairsStep-by-step explanation:Let the complete question is,"Last Thursday, John assembled chairs at a rate of 3 chairs per hour for part of the day and Larry assembled no chairs. Last Friday, Larry assembled chairs at a rate of 4 chairs per hour for part of the day and John assembled no chairs. If John and Larry assembled chairs for a total of 7 hours during these two days, how many chairs did John assemble last Thursday if  during these two days, John and Larry assembled a total of 25 chairs."Let last Thursday, John assembled chairs for x hours and last Friday, Larry assembled chairs for y hours,So, total number of hours = x + y∵ total hours of working = 7,⇒ x + y = 7,    .....(1)Rate of assembling chairs for John = 3 chairs per hour,Thus, the total chairs assembled by John = 3x,Similarly, Rate of assembling chairs for Larry = 4 chairs per hour,Thus, the total chairs assembled by Larry = 4y,Total assembled chairs = 3x + 4y∵ Total assembled chairs = 25,⇒ 3x + 4y = 25      .....(2)Equation (2) - 4 × equation (1),3x - 4x = 25 - 28-x = -3⇒ x = 3Hence, The number of chairs assembled by John last Thursday = 3(3) = 9