The equation is given as 4 - 0.25g + 0.5h
The values of the unknown variables have now been given as g = 10 and h = 5
At this point all you need do is substitute for the values of the unknown (since they've now been given a known value). When g = 10 and h = 5, then the expression becomes;
4 - 0.25(10) + 0.5(5)
4 - 2.5 + 2.5
[Note that 0.25 times 10 = 2.5 and then 0.5 times 5 = 2.5]
Applying the rule of PEMDAS [Parenthesis, Exponent Multiplication Division Addition and Subtraction] the addition will be given preference. Hence the expression becomes
4 - (2.5 + 2.2)
4 - 5
-1
The final answer is -1
Note that if the rule of PEMDAS was not applied, the answer would differ because it would now become;
4 - 2.5 + 2.5
1.5 + 2.5
4