WACC=WdRd(1-Tc)+WeRe
Plug in values
WACC=[100/(25+125+100)]*10%*70%+[(25+125)//(25+125+100)]*40%*(24%-10%)
Above, the weight of debt and equity is allocated according to the market(leveraged) value independent of cash and fixed asset and the tax rate and cost of debt are given, so the only problem is the cost of equity. The text indicates that the cost of equity can be regarded as the expected rate of return, subtracting LIR (loan interest rate) from RoS.

WACC=WeRe+WdRd(1-Tc)=[(25+125)/(25+125+100)]*(24%-10%)+[(100)/(25+125+100)]*(10%)
We is calculated through dividing equity by the sum of equity and debt and Wd is the ratio of debt to the aggregation of equity and debt. Obviously, tax rate and cost of debt are given. The only problem, Expected rate of earning (cost of equity) is derived from subtracting LIR from RoS.