2(v-h)/k=r solve equation for v in terms of all other variables involved

2(v-h)/k=r
(2v-2h)/k=r
2v-2h=r·k
2v=r·k+2h
v=(r·k)/2+h

You need to divide 210 square inches by 35 inches and that’s going to give you 6 inches and that’s the length of the hypothenuse of the right triangle i hope that this you : )