Quarterly billing for water usage is shown below.

Year

Quarter 1 2 3 4

Winter 64 66 68 73

Spring 103 103 104 120

Summer 152 160 162 176

Fall 73 72 78 88

The forecast equation is:

Ft = 64.875 - 6.1375 Qtr1t + 32.325 Qtr2t + 86.0375 Qtr3t + 1.2875 (t).

Forecast the summer of year 5 and spring of year 6. *If using formulas is excel please show!