A board that is 1.5 m long is supported in two places. If the force exerted by the first support is 25N and the force exerted by the second is 62N, what is the mass of the board?

I assume that the whole system is at rest.

If this is the case, then what conclusions can you make about the total upward force compared to the total downward force?

Assuming that the system is at rest:

"_" - subscript

F_total = 25N + 62N = 87N

Now use the formula F_g = ma and rearrange it

m = F_g / a

Note: a = g = 9.81m/s^2

m= (87N) / (9.81m/s^2) = 8.9kg