His estimate is reasonable. But only if Michael is less than 2 years old.
1st one is the y Intercept is 5. get y by itself 12y=-6x+60 divide by 12.
2nd slope is -3
Check the picture below.
they're at a 3:1 ratio, thus, 3 times.
If you want to find the total in the bank account after the 6 withdrawals it would be a -$68.