1) The formula for the final amount A in an investment with principal P and interest I (A=P+I. Determine the principal if A is $7,000.00 and I is $400.00 - is my answer correct

Question

1)  The formula for the final amount A in an investment with principal P and interest I (A=P+I.  Determine the principal if A is $7,000.00 and I is $400.00 - is my answer correct

7,000.00 =  P + 400.00
P = 7000.00 - 400
P = 6600.00

2)  There is a diagram of figure and am asked to find what x is.  The perimeter is 24.  One side is 4x, another side is 3x + 1 and the other side is 2x - 5.  Please help. Txs