In the first part, we have the followed expression:
[tex]5x\text{ - 15}[/tex]Wants to know the value of it when x=10, so we just need to substitute the value in the expression, wich gives us:
[tex]5\times(10)\text{ - 15, wich give us the expression: 50 - 15 = 35}[/tex]In the second part, we have the expression:
[tex]\frac{1}{2}b\times h[/tex]And we want to know the value of it when b=5 and h=6, so lets substitute those values in our expression:
[tex]\frac{1}{2}(5)\times(6),\text{ wich gives us, }\frac{1}{2}30\text{ = }\frac{30}{2}\text{ = 15}[/tex]