the number of points issac scores for collecting treasures is Y

$E[a X + b] = a E[X] + b\\ \\ Var[a X + b]= a^2 Var[X]\\ \\ E[Y] = E[100X-50] = 100E[X]-50\\ \\ Var[Y] = Var[100X-50] = 10000Var[X]$

I bet you have E[X] and Var[X] from some other part of the problem so plug those in.