Write a function howManyMonths$($start$,$ rate, spending, target$)$ where:

start $-$ the starting balance in your bank account $($float$)$

rate $-$ the monthly interest rate $($float$)-$ like $0\mathrm{.}001$ for $0\mathrm{.}1\%$

spending $-$ the monthly amount that is spent each month $($float$)$

target $-$ the target savings that you'd like to achieve

The function returns how many months it takes to save the target savings amount. The function should return a $-1$ if the balance goes below $0$ because the spending is too high. The function should also return $-1$ if the target is not reached after $100$ months.

Each month you earn the monthly rate of interest, but you also spend the spending amount.

So$,$ next$\_$month$\_$balance $=$ start$\_$balance $*(1+$ rate